Here are the steps to build a potato gun:

1. Materials you will need:
- A syringe
- Electrical tape
- A metal tube
- A piece of chopstick

2. Attaching the Barrel to the Syringe:
- Use electrical tape to firmly attach the metal tube to the part of the syringe that sprays whatever is in the syringe.

3. Strengthening the Barrel:
- Attach the piece of chopstick to the end of the syringe and the metal tube.

4. Shoot Your Potato Gun:
- Pull the plunger of the syringe to maximum length without disconnecting the two pieces.
- Hold the barrel about a cm away from the open end.
- Stab the end into the potato a cm deep.
- Twist the barrel inside the potato so that the piece breaks off.
- Pull the barrel out of the potato and point at whatever you want to shoot at.

Another way to build a potato gun is by using PVC pipes. Here are 15 easy-to-follow steps on how to make one:
1. Assemble your potato gun using a 3 in (7.6 cm) wide PVC pipe (14 inches (36 cm) long) as the main chamber.
2. Attach a 4 ft (1.2 m) long 1.5 in (3.8 cm) wide PVC pipe to the chamber using a coupler and reducer to form the barrel.
3. Install a spark generator or BBQ ignition switch to the chamber to make the trigger.
4. Potato guns are dangerous so be careful when using them.

I hope this helps! Let me know if you have any other questions or if there's anything else I can help you with.