Look at the position, memorize it and set it up again from memory.
Strong players remember a position at a glance: they see familiar patterns, not separate pieces. This memory helps calculation, because the position a few moves ahead stays in front of your eyes.
The trainer shows a position for a few seconds. Then the board is empty: set the pieces up again, find where a piece is, or name what stands on a square.
In groups, not piece by piece: first the kings and their shelter, then the big pieces, then the pawns. Say it to yourself: white king g1, pawns f2, g2, h2.
Yes. Pick a piece in the panel under the board and tap squares, no dragging needed. The eraser removes extra pieces.
Yes, the trainer is free and works without sign-up.