My 99 Grand Prix 3.8 . The starter engages but doesn't turn the flywheel.can anyone tell me what wires go where?

If you look at the back of the starter:

The main wire from the battery (and probably two others with large eyelets) go to the top post on the solenoid (the black part on the top). The main starter wire (the one which energizes the solenoid and thus the starter) should connect to the smaller post on the right of the solenoid. (NOTE: This wire is most likely purple in color ... at least that's what GM's been using for years now, I suspect it will be the same for your Grand Prix.)

If the starter is spinning, but not engaging, it means the starter gear isn't going completely into place and meshing with the flexplate. If it's spinning, there's nothing wrong with the wiring. In order for the motor to spin, the internal parts of the solenoid are working correctly. Either something is getting in the way of the starter gear or the starter is not aligned correctly. There is an outside chance the battery voltage may be low, but I'm doubtful of this.