The MOSFET will connect to the Circuit Playground Express using the STEMMA port. 

Connect the STEMMA cable to the Circuit Playground Express as follows:

• Black wire --> GND
• White wire --> A1
• Red wire --> VOUT

The air pump connects to the spring terminal on the MOSFET, connecting + to + and - to -. Look for a little red dot on the back of the pump near one of the solder terminals to tell which is which. The side with the dot is +.