Player1 clicks the board to allow Zillions to create a random setup.
Then Player1 and Player2 alternate clicking 16 pieces (namely 1 King, 1 Queen, 2 Rooks, 2 Knights, 2 Bishops, 8 Pawns) which will turn black. (You can click function key F7 on your keyboard to check what pieces are left to click.)
The resulting chess position should have neither King being attacked. (This is NOT checked by the program!)

A sign saying 'Player 2 : please choose colour' will appear at the right border. Now Player2 clicks either a black piece to confirm the selection by Player1 or clicks a white piece. In the latter case all white pieces will turn black and vice versa.
After this step normal chess play starts with Player1's move. Both players play standard chess moves. The only exception is that you win by capturing the opponent's King.

Variant 2:
Like variant 1, but Player2 will not be able to choose (after the setup has been completed) which colour he/she wants; i.e., the pieces keep their colour and Player2 will always play Black.

Please note that there is an alternative piece set available.