After lots of experimentation and confusion, western countries ended up with the chromatic scale with a 12 equal temperament tuning. If you produce modern pop music, this is the only scale and temperament you will ever use.
Scale
A scale is a set of defined pitches. The chromatic scale defines 12 pitches, we will call notes from now on. All modern western music is based on these 12 notes. This definition of the chromatic scale is also the reason why a piano keyboard is grouped in multiple sets of 12 keys.
You see in the illustration above that the same 12 notes repeat over the whole keyboard. The reason for this repetition is how humans perceive frequencies. More about this later.
Musical Notes
From now on, we will use the term note for a sound in one of these 12 defined pitches. In the English language, the term note stands for the pitch of a sound, but also for the symbol in musical notation ♩. As we will not discuss the musical notation in this document, we use the term note for a sound at a defined pitch.