When you are happy everything is correctly wired up on the circuit board connect up the search coil, the small coil and the tuning capacitor. Make sure that you are outside, the search coil is not resting on a metal surface and for this initial test it should be supported in the air and off the ground. Listen to the earpiece and while doing so adjust the tuning capacitor till you hear a note.

If you can hear a note, try putting a large metallic object such as a hammer near the search coil. You should hear the note change - congratulations you have a working metal detector!!