what do u mean by current block?

A block is a set of statements that are contained between a pair of braces. Blocks can be associated with subroutines, loops, conditionals and a number of other Perl constructs. There is also an implicit block around all of the code in a file.

our (like my) is lexically scoped, this means that its effects are only felt until the end of the innermost enclosing block.

I understand "my" is used for local variable.
so is "our" a global variable??

Pretty much. It exposes package variables within a given block. The differences between package and lexical variables and the subtle differences between my, local and our can get a little complex. I recommend you read the section on "Scoped Variable Declarations" that starts on p130 of the 3rd edition of the Camel.

"The first rule of Perl club is you don't talk about Perl club."