they have a padded chamois in them, to cushion the ride. You wear these w/o undies cause if you do, you're likely to have trouble with chafing and stuff.

You might also need to use some "butt balm" of some sort. I've seen recommendations of apply diaper cream to the affected areas. There are others made specifically for cycling.

I'm sure that the other, far more experienced folks will chime in here, but I bought a couple pair of shorts and have had no trouble at all.