Switches into Plate
First, insert a couple of keyswitches through the keyswitch plate. The plate mechanically connects the switches to each other, which lends some nice lateral stability to the keys.
Connect to Board
Carefully press the two switches into the switch sockets, being very careful to align the legs so none bend!
Now, you can add your keycaps! simply press them onto the keyswitch stems until they are fully seated.