I want to be able to train my mating skills by making a chess engine play positions that others have resigned from. Is there a way to make a chess engine play a particular position? I am using stockfish and scid vs pc at the moment.
In Scid vs PC got to Edit > Setup Board. Here you can setup the board with a particular position, set side to move and castling flags. Easier is if you have a FEN of the position, you could just paste this and use it directly. Click OK once you are done to get the position on the main board.
Now navigate to Play > Computer-UciEngine > Choose your stockfish engine, Check "Start from current position", Set desired time control and click "Play".
I have no specific knowledge about stockfish, but usually there is an Graphic User Interface (GUI) to a chess engine. The GUI allows you to edit a game (making moves---do this because it takes care of fine details like castling rights and right to en passant) or edit a position (placing pieces) and than let the engine play.
You can specify who is on the move and which colour(s) the engine should play independently.