Learning...

Okay, I'm trying to work some PHP into a page I maintain, but I'm still very new to the concepts involved in PHP. This is probably really simple, but I can't find directions anywhere so I'm hoping all you PHP smarties can help. This is what I want to do:

I want to write one document that defines a few variables and I want to call those variables from several other pages. How do you call a varible that is defined in another document?

Thank you in advance!