Ok, what is a PDF? No, it doesn't really stand for pretty darn funny. That was just to get your attention!
PDF stands for portable document format. So think that through. Portable - easy to carry or transport. Document - something created in word processing or spreadsheet or other software. Format - the way it is created. So a pdf is a file that can be moved from one computer to any other computer without having software compatibility issues. Word documents, Comic Life documents, AppleWorks documents can all be saved as PDF's so they can easily be transferred to other computers via email, ichat, flash drives, CD's, etc. These documents can be created on a Mac and still be opened on a PC, and vice versa.
Simply (yes, I really mean simply!) create the document in whatever software you want. Save the document but don't close it. Now pretend you are going to print the document - File/Print.
See the button that says PDF? Hold that down and choose 'save as pdf.' That's it! Now you can send the pdf file via email and the recipient will be able to read it. You need to know that a pdf is read only. The recipient will not be able to edit the document, only read it. This is very handy to know if you want to send out a newsletter to the parents of your students. You can create an awesome looking newsletter in Pages, then save it as a PDF, and send it to them through email. Most of them may not have Pages, but that doesn't matter anymore if you save it as a pdf.