How do I use Microsoft Office Mobile on my smartphone?

I got a smartphone from ATT about a month ago and have been trying to figure out how to view PowerPoint presentations and Word documents with the Office Mobile application. Is there a certain format I have to save them in before I put them in my documents in my phone’s memory? I’ve tried just saving it as I usually would and copying to my documents, but they don’t show up on the phone that way. Any help?