You would probably best be served by getting a text editor that allows you to run your programs from the editor. Personally I use ConText - syntax highlighting and it's free, plus it lets you set up the function keys to run your Perl programs and lets you see the text output in the bottom window - but there are many others to choose from. Search on here and you'll get many opinions.

That said, the short answer is use the cd command to change to the directory your program is in, and in addition make sure that Perl is in your path - ActiveState should have done that for you I believe. That should do the trick.

Since you're not that good with DOS you'd be best to do a Google search for DOS commands or a DOS tutorial.

Good luck!