Here's an unbelievably crude guide to how to find a variant game in the Play area.
As for the computer, can't do that here. There are sites that let you like lichess or pychess, or you can find software that supports Chess960, like Arena.
Where to play Chess 960 online against the computer or others?
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Ive been looking for a place to play with the random pieces against the computer or others.I thought Chess.com said they have it but I couldnt find it. Is it online?