Chords are simply groups of notes played at the same time. Arpeggios are the notes of a chord played one at a time.
A brief definition
Chords made up from the 1st, 3rd, and 5th notes of the scale. This is a basic introduction.
Chords made up from the 1st, 3rd, 5th and 7th note of the scale. This is also a basic introduction.