What is solo chess?

Please tell
Oddly i get possitions like this

You just have to capture all the pieces.

Yes 

You have to capture your own pieces 

You have to progressively capture all the pieces except one. It doesn't matter which one is left unless there's a king on the board, then it has to be the last piece standing. It's kind of like those peg puzzles you see on the table at Cracker Barrel. 

The first few puzzles are very easy, and you think, "Hey, this is a piece of cake." But then they start to get fiendishly difficult. If you start with the wrong piece, there's no way you can have only one left at the end. So you really have to look ahead and calculate where you're going to go. Yes, all the pieces are white simply because you're not playing against anyone; you're challenging yourself to have the fewest pieces at the end.

When starting a round of solo chess in a web browser, you should see the following rules popup on your screen. In the iOS app, the rules can be found in the drop-down menu by hitting "help."

While most of the rules have been explained in the replies above, it's also important to note no piece can capture more than two times per puzzle.