I have a simple question, but I just want to make sure I did this right.

I'm using MS word for Mac 2008.

I need to have an 8.5 x 11 sheet. It's a manuscript for a book that I wrote. My question is, how do I check, to ensure that it's 8.5x11? I don't know how to adjust this, or even check this.

Thank you so much!