you may both right- and leftclick the mouse.
To make a lead leftclick on the card. To lead several cards at a time
use the right mouse button. The lead is only performed in case you have
2 or 3 cards of the same value. For the computer to beat all of your
cards, leftclick on any of your cards, or else press the lead key. While
playing the “Transfer Fool” to transfer the lead use the left mouse
button. To beat a card, use the right one. In case the burned cards may
be returned in the course of the game, leftclick on the burned cards and
they’ll get back to you.