Q: How to stop last site from popping up when turn on computer?

Hi James L. Conner!

I believe that the feature you are speaking of is referenced in the following article:

OS X Mavericks: Using the power button

http://support.apple.com/kb/HT5869

Accessing the Shut Down Dialog

Press and hold the power button for 1.5 seconds, to bring up additional options:

Just be sure to uncheck the box that is next to “Reopen windows when logging back in,” and you should see a cessation of this feature. Thanks for using the Apple Support Communities!

Cheers,

Braden