Step 8: Add the transistors
This board uses two transistors to amplify current, one for the speaker and one for the LED array. Both transistors are the same, so you can't mix them up.
However, they are both oriented differently! Note the proper orientation in the picture. Slot in the transistors, then flip the board over and solder them in. These little guys like to slide out of the holes while you're soldering, so it's easy to end up with the transistor standing taller than you expected. This isn't an issue, but if you notice while you are soldering the first leg, it's easy to put a little pressure on the transistor from the other side of the board with your finger, heat up the leg so the solder reflows, and push the transistor down. When you remove the iron, the transistor will usually stay put.
When you're done soldering the transistors, cut their legs short.