I'll add two things to roboticus' excellent treatment:
Firstly, be careful with backticks when you want your your script to run on different systems as it always runs a "system shell" and that may not be the same shell on different systems.
And secondly there is another syntax for backticks, which is qx. The advantage of qx is that you can choose your own delimiters, so e.g.
my $result = `command`;
can also be written as
my $result = qx| command |;
which I find nicer, though your taste my of course be different.