Unless your guitar uses batteries you have ‘passive’ tone controls.
These will be found on your basic tele, strats, Les Pauls, etc. This means that when the tone knob is on 10 it’s not boosting or adding anything. When the knob is turned down the treble frequencies are subtracted or cut.
Many players leave their tone on 10 and that’s it. I almost always find myself working the tone controls to get that desired sound. I use a tele and that is a guitar with an extremely bright sound. Cutting back on the tone mellows it out enough for playing jazz or finger style arrangements.
Whatever guitar or style of music you are playing, learn to work your tone knob. Turning it down different degrees can give you more variety in your sound.

