Your problem description is rather vague. Is this what you were after?

(By the way, it is helpful to provide a COMPLETE, RUNNABLE example of your code so people don't have to fill in the boilerplate just to look at what you are trying to do.)

UPDATE: Er... removed spurious message code from example. Copy/paste error :/

use strict;
use warnings;
use Tk;

my $mw = MainWindow->new;

my $fsdb_tab     = $mw->Frame()->pack( -expand => 1, -fill => 'both' )
+;
my $button_frame = $mw->Frame()->pack( -expand => 1, -fill => 'x' );

#### Label & Entry creation to select the test path
my $frm_name = $fsdb_tab->Frame()->pack( -side => 'left', -fill => 'bo
+th', -anchor => 'n' );
my $lab = $frm_name->Label( -text => "TEST PATH:" )->pack( -side => 'l
+eft' );
my $ent = $frm_name->Entry( -width => 80 )->pack( -side => 'left' );
$ent->focus;

#GUI building for Browser push buttons
my $but = $frm_name->Button(
    -text             => "Browse",
    -command          => \&browser_button,
    -activebackground => 'lightblue',
    -activeforeground => 'black',
    -relief           => 'raised',
    -borderwidth      => 8
)->pack( -side => 'right' );

#### Button for "Run FSDB"

my $final_frame =
  $button_frame->Frame( -borderwidth => '5', -relief => 'ridge' )
  ->grid( -row => 0, -column => 0 );
my $run_fsdb = $final_frame->Button(
    -text             => "Run FSDB",
    -command          => \&run_fsdb,
    -activebackground => 'lightblue',
    -activeforeground => 'black',
    -relief           => 'raised',
    -borderwidth      => 8,
    -width            => 10
)->pack( -side => 'left', -expand => 0 );
#### Button for "Refresh"
my $refresh_frame =
  $button_frame->Frame( -borderwidth => '5', -relief => 'ridge' )
  ->grid( -row => 0, -column => 1 );
my $refresh_fsdb = $refresh_frame->Button(
    -text             => "Refresh",
    -command          => \&refresh_fsdb,
    -activebackground => 'lightblue',
    -activeforeground => 'black',
    -relief           => 'raised',
    -borderwidth      => 8,
    -width            => 10
)->pack( -side => 'left', -expand => 0 );

#### Button for "EXIT"
my $exit_frame = $button_frame->Frame(
    -borderwidth => '5',
    -relief => 'ridge'
)->grid( -row => 0, -column => 2 );

my $exit_fsdb = $exit_frame->Button(
    -text             => "EXIT",
    -command          => sub { $mw->destroy; exit; },
    -activebackground => 'lightblue',
    -activeforeground => 'black',
    -relief           => 'raised',
    -borderwidth      => 8,
    -width            => 10
)->pack( -side => 'right' );

MainLoop;
[download]

Here is the complete code. Click on the "FSDB Configuration" tab.

Here i am unable to get the 3 button's in a new line

#!/usr/bin/perl

use Tk;
use Tk::Text;
use Tk::BrowseEntry;
use Tk::DirTree;
use Tk::NoteBook;
use File::Basename;

my %manager_hash = (
                      "all"      => "Sheet 2",
                      "fsdb"     => "Sheet 3",
                    );

######################################################################
+##################
##################################### MAIN  GUI ######################
+##################
######################################################################
+##################

my $mw = MainWindow->new(-title=>"FSDB And Manager Launcher");
$mw->geometry( "900x270" );

#### Creating the tabs in the GUI
my $book = $mw->NoteBook()->pack( -fill=>'both', -expand=>1 );

my $select = $book->add( "Sheet 1", -label=>"Manager Selection", -crea
+tecmd=>\&create_managerTab );
my $all_tab = $book->add( "Sheet 2", -label=>"All configuration", -cre
+atecmd=>\&getAllTab, -state=> 'normal' );
my $fsdb_tab = $book->add( "Sheet 3", -label=>"FSDB configuration", -c
+reatecmd=>\&getMainTab, -state=>'normal' );

MainLoop;

######################################################################
+##################
##################################### GUI Functions ##################
+##################
######################################################################
+##################

sub create_managerTab {
        
    #### Radio buttons for Manager selection
    $frm_manager = $select -> Frame(-borderwidth => '3', -relief => 'r
+idge') ->pack();
    $lbl_manager = $frm_manager-> Label(-text=>"SELECT THE MANAGER'S T
+O RUN: ")->pack(-side => 'left');
    $manager = "all";
    $rd_all = $frm_manager -> Radiobutton(-text=>"All",  
           -value=>"all",  -variable=>\$manager)->pack(-side => 'left'
+, -expand => 'y');
    $rd_fsdb = $frm_manager -> Radiobutton(-text=>"FSDB",  
           -value=>"fsdb",  -variable=>\$manager)->pack(-side => 'left
+', -expand => 'y');


    $select->Button( -text=>'OK', 
                     -command=>\&enableTab, 
                     -font => 'Times 12', 
                     -activebackground => 'lightblue',
                     -activeforeground => 'black',
                     -relief => 'raised',
                     -width => 20, 
                     -borderwidth => 5)->pack();

    $select->Button( -text=>'Exit', 
                     -command=>sub { $mw->destroy; exit; },
                     -font => 'Times 12', 
                     -activebackground => 'lightblue',
                     -activeforeground => 'black',
                     -relief => 'raised',
                     -width => 20, 
                     -borderwidth => 5 
                      )->pack();
    
}

#################################################################
#    This function is used to enable/popup the perticluar tab   #
#    selected in the "Manager selection" tab                    #
#################################################################
sub enableTab {
    print "MANAGER ===> $manager\n";
    $book->raise("$manager_hash{$manager}");
}

    
sub getMainTab {
    #### Label & Entry creation to select the test path
    $frm_name = $fsdb_tab -> Frame()->pack(-side => 'left', -fill => '
+both', -anchor => 'n');
    $lab = $frm_name -> Label(-text=>"TEST PATH:")->pack(-side => 'lef
+t');
    $ent = $frm_name -> Entry(-width=>80)->pack(-side => 'left');
    $ent->focus;    

    #GUI building for Browser push buttons
    $but= $frm_name -> Button(  -text=>"Browse",
         -command =>\&browser_button,
         -activebackground => 'lightblue', 
         -activeforeground => 'black',
         -relief => 'raised',
         -borderwidth =>8 
       )->pack(-side => 'right');

    #### Button for "Run FSDB" 
    $final_frame = $fsdb_tab -> Frame(-borderwidth => '5', -relief => 
+'ridge')->pack();
    $run_fsdb = $final_frame -> Button(  -text=>"Run FSDB",
         -command => \&run_fsdb,
         -activebackground => 'lightblue', 
         -activeforeground => 'black',
         -relief => 'raised',
         -borderwidth => 8,
         -width => 10
      )->pack(-side => 'left', -expand => 0);

    #### Button for "Refresh"
    $refresh_frame = $fsdb_tab -> Frame(-borderwidth => '5', -relief =
+> 'ridge')->pack();
    $refresh_fsdb = $refresh_frame -> Button(  -text=>"Refresh",
         -command => \&refresh_fsdb,
         -activebackground => 'lightblue', 
         -activeforeground => 'black',
         -relief => 'raised',
         -borderwidth => 8,
         -width => 10
      )->pack(-side => 'left', -expand => 0);


    #### Button for "EXIT"
    $exit_frame = $fsdb_tab -> Frame(-borderwidth => '5', -relief => '
+ridge')->pack();
    $exit_fsdb = $exit_frame -> Button(  -text=>"EXIT",
         -command => sub { $mw->destroy; exit; },
         -activebackground => 'lightblue', 
         -activeforeground => 'black',
         -relief => 'raised',
         -borderwidth => 10,
         -width => 10
      )->pack(-side => 'right');
}
[download]

Sammy..

The technique thundergnat demonstrated is to use a container widget(Frame) with a grid sizer (or whatever), so just copy/paste that and you're good to go