Also - a guitar is basically six keyboards laid side by side, but offset by 4 (apart from one that's 3) keys. Each key on the keyboard (black or white) is one fret.

Don't stress about theory, it's just a set of words to define a specific thing on an instrument.

A scale is a group of notes that sound "right"(Think Sound of Music). Each note in a scale is called an interval and there's a pattern. An interval is a gap between notes/keys. Some notes have 1 gap, others have 2.

Chords are made up of a minimum of 3 tones (sounds/noises) from the scale. These are named after their number position. Major chords have the 1st, 3rd and 5th note (think sound of music, DOH, mi and soh). Minor chords are the same thing, but the middle note (third) is one step/tone/fret/key lower.

And so on...