Playing against the computer

Does anyone know of a website where I can create a position and play against the computer. I would like to do it here at chess.com but it doesn't look possible. I'm reading Silman's Endgame book and created a database of the diagrams in the book and want to practice when I'm away from home. It's been great doing it at home with Chessbase's Komodo interface but I want to be able to do this when I'm away from home as well.

Thanks to all!

chess.com is possible on mobile though

You can download install Droidfish on your mobile device. You can set up any position to practice playing.

Thank you to all! Probably going to use both but mainly the lichess.org. Seems like a pretty good interface.