A Major triad has a "large" interval (Major 3rd) at the bottom, while a Minor triad has a "small" interval (Minor 3rd).
A (Semitone) is the smallest distance between two notes (e.g., C to C#).
Try to associate intervals with famous songs (e.g., the first two notes of "Star Wars" is a Perfect 5th).
The top number tells you beats are in a measure (e.g., 4).
A is the "home base" of a song, and a Scale is the sequence of notes within that key.
Before you can build a scale, you need to know the distance between notes.
A (Whole tone) consists of two half steps (e.g., C to D).