Paper in Oil capacitor 0,068 uF 500V Russian military grade

Electricity, and with it the electrical frequencies from the pickups, follows the path of least resistance. If your potentiometer is off, the signal flows to earth, if the potentiometer is open, then the signal goes to your jack and from there to your amplifier.

Now you can put a resistance or capacitor on a potentiometer with which you make a bypass so that the signal, when you turn the potentiometer off, goes via the resistor to the jack. If you open your potentiometer further, more signal will go through the potentiometer and less via the capacitor. That way you create a tone pot.

A capacitor allows lower frequencies to pass through, but offers resistance to higher frequencies. If you let your whole signal run through the capacitor, the - for that type of capacitor - most highest frequencies are blocked and you get the lowest, most bass sound. As you open the potentiometer further, more frequencies are transmitted to the jack and you have more treble in your sound.

These are the most used values and applications of capacitors that could be uses as a guideline, but there are many factors that influence the final sound and tone range such as the pickups, the potentiometers, the amp and settings and your taste.

0.015uF: for neck position humbucker guitar
0.022 - 0.033 uF: for humbuckers guitar
0.047uF: for single coils and some basses
0.068 - 0.1uF: for basses