The circle of fifths is an excellent music theory graphic that every musician should know inside and out. It shows you all the notes in any major or natural minor scale and the key signature for each of those scales. You can also use it to build the triads in the major scale, as well as use it for transposing and modulation.
There are a number of different systems of music notation for the guitar. Those systems are standard treble clef, lead sheets, guitar tab, chord charts, chord diagrams, Nashville numbers, and Roman number analysis. I explain each type, have graphics for each, cover how to read and use each of them, and have PDF files free for download.
If you want to know what a triad is in music then the answer is here. I give the definition of the four basic music triads: major, minor, augmented and diminished. Triads in music are the basis of all harmony and I have open and closed guitar chords for all the types of triads in music.
Music intervals and the chromatic scale are the results of dividing an octave into 12 equal parts known as semitones. Once you know all of the music intervals, then you can build any scale or chord based on the intervals that comprise them. Intervals and the octave are fundamental aspects of music theory and are easy to understand.
Learning and practicing the notes of the chromatic scale on guitar is crucial for speed, dexterity, fretting & picking hand coordination. It also helps you learn the notes at every fret on every string. I define the chromatic scale and its notes in a few different ways. I also have some practice exercises and graphics to help you learn this scale.