I have a 1280 x 1024 monitor I want to use as display. I have an HDMI to DVI adapter. What must I configure to make it work?
You shouldn't need to configure anything. Because you said you have a HDMI to DVI adapter, I am assuming your monitor is DVI. So just plug the pi's HDMI into the monitor (using the adapter) before turning the pi on and then turn on the monitor and then the pi and it should work.
If it doesn't you may need to force the HDMI connection. Put the SD card in your computer and edit the config file in the boot partition, as described here.
More ways to edit the HDMI configuration can be found here. (Thanks, Jaromanda X.)