I am pretty new to perl and this might be a stupid question
Actually, if anything, the question is probably harder to answer than it needs to be, because of the confusing way in which you stated it. Nonetheless, I'll try...
how can i separate my code in pieces and run them all from one file
There are several ways to go about this, depending on what it is you want to accomplish. do '/path/to/filename.pl' for instance is not entirely the same as require '/path/to/filename.pl'. (One difference is that the latter won't run the contents of the file twice if you have the same require statement in two different places.) For a beginner, require may be close to what you want, but it's hard to be sure without knowing more about your situation. Be aware that the required file should finish with a true value. There is also use, of course, not to mention various more obscure possibilities (such as open FOO, $filename and eval scalar <FOO>).