The game is a two-player game. Player 1 chooses one of the 16 pieces.
Player 2 then places this piece on one of the 16 squares of the board
and chooses a piece out of the remaining 15 pieces which he gives to
player 1, who places this piece on one of the remaining 15 squares on
the board, etc...

Xquarto supports three different player combinations: human vs
computer, computer vs human and human vs human (possibly through the
local network in the latter case). The default combination is human vs
computer, i.e. the human player starts the game against the computer.
This can be changed by clicking on the "Actions" menu (see below for
more details).