They are set into the "autopilot" as far as getting to the range. Of course, you can just look at the Map, too. The targets are up to you to select. Look at the ground, pick something you want to hit, then hit it. The cloud deck is low enough that it will de-select most targets anyway as you pull up to drop again. So, it's up to you to decide.
In reality, they tell you what you are to bomb and how in lengthy briefings for numerous trips out to Gila Bend and back. The Range is a duplicate of the real deal. Some of those targets were for big nuke bombers. You cannot just shoot what you want because there are people out there on the ground.