A triad is a root, a third and a fifth stacked together. If the third is a minor 3rd the chord is minor; a major 3rd makes it major. Add the 7th for colour — maj7 is dreamy, min7 is soulful, dominant 7 pushes toward resolution.
In Roman numerals, capitals are major (I, IV, V) and lowercase are minor (ii, vi). The workhorses: I–IV–V (house and pop), I–V–vi–IV (the endlessly catchy “pop” loop), and ii–V–I (jazzy and sophisticated). Most hit songs use only three or four chords.
Loop your progression over 4, 8 or 16 bars, and start the bassline on the root of each chord. Emotion and flow beat complexity every time.