A group of notes that work well together

These are basically all twelve (12) notes in an octave. The naturals (7) and non-naturals (5) together make up the chromatics. (7+5=12)

The notes that do not have sharp or flat names (A, B, C, D, E, F, G). There are seven (7) of them.

The notes that do have the sharps or flats in their names (A#, C#, D#, F#, G#). There are five (5) of them. These notes are also often called the "accidentals".

Sharp generally just means higher. Sharp of the note you are on would be one note higher. To tune sharp you would tune "up".

Flat generally just means lower. Flat of the note you are on would be one note lower. To tune flat you would tune "down".

This is a type of scale or chord that sounds bright, happier, and more upbeat. It has no flats in it. This is kind of subjective, and will be explained much more in-depth in the lessons.

This is a type of scale or chord that sounds darker, maybe more sad, kinda gloomy. Minor scales or chords do use flats. This is kind of subjective, and will be explained much more in-depth in the less [..]

This is basically the same thing as "key". The root note is the note that the music is centered on or built from. You could say its the "main note" in a song.

A key is a group of notes and chords built on the notes of a scale, centered on the root.