First, click the "list of tables" link. It appears in the lower left corner of the home page, and is surrounded by a green box in the screenshot below:
choose your partner at World of Card Games |
The list of tables shows you that there is a "Registered" player at a Spades table. (The green "R" stands for registered.)
To be their partner, click on the 3rd white square in that row. That white square indicates an empty seat. In the screenshot, the "seat" is highlighted by a green box.
Once you click on that square, you will be taken to the seat across from the registered player.
You have to be quick! If someone else takes the seat before you can click it, you won't be able to sit there.