When a module is use-ed, it can be passed a list of scalar values, strings or numbers, for the module to do with as it pleases (well, as the programmer has defined, hopefully). So in the statement
    use Foo::Bar qw(func1 func2);
the Foo::Bar module is passed the list of strings 'func1' and 'func2'. In the case of
    use Test::Simple tests => 1;
the module Test::Simple is passed the values 'tests' and 1 (although the latter value may be passed as a string; I'm uncertain on this point). The  => (fat comma) simply insures that  tests is interpreted by the compiler as a string when generating the list. (In fact, I think the statement
    use Test::Simple qw(tests 1);
would work just as well, but I have not tested this.)

Update: See Perl Modules in perlmod; also see perlmodlib.