My sites are fairly simple.
I prefer to keep them to 800 wide and have them centered.
I have not been able to figure these two criteria for my design.

Any ideas of how to center the webpage and limit the width to 800 pixels would really help.

Thanks,

On the Properties tab set your Grid's Max-width to 800px.
Then set your left and right margin to auto for elements. You have to change the Display setting to Block for some elements.

CC gives you lots of choices. Eric's suggestion fits exactly what you asked for.

Just in case you want a top navigation bar or a bottom footer that stretches all that way across the screen (which it doesn't sound like you want, but just in case)...

If you set your grid to max-width of 800px, none of your site can expand its width beyond that. An alternative is to have no max-width for the rows that stretch across the screen and set the other rows' max-width to 800px. This allows you to have a particular row (such as your navigation menu or your footer) stretch all the way across while the rest of your site stays within your 800px width.