To play a move : cursor is a red U frame; move it to the source square, press Enter. The frame is now green color; move it to the target square, press Enter, it is back to red color. Now press space bar to complete the move (or back-arrow to cancel).

Shift-Enter looks indeed to be an alternative to validate the target square, instead of Enter then space bar. But it prevents canceling (back-arrow).

Level : it is selected thanks to the file (column) you select after entering time mode (T key).

Hitting 1 to 4 does not set the level, it sets the variety. There is just a short beep that can be hardly heard, as an acknowledgement.

I found out the english version of the help file is here, early in this very same thread. It should be helpful.
MfG,
Eric