Chess · Stage 1: Don't hang pieces

Is this move safe?

This one question, asked before every move, saves more games than any opening.

Already know this? Take the check: just the questions, no reading. Get them all right first time and the lesson counts as done.

A move is safe if, straight after it, your opponent cannot win material or give mate. Count each exchange. A cheaper piece taking a dearer one wins, even if you can take back.