The basic elements you really need to know to get started is the major scale. You have to know it in all 12 keys. Once you have that down then the chords can be pulled from your knowledge of that scale. If you number all the notes of the scale then a
Major Triad is 1,3,5
Major 7th is 1,3,5,7
Minor Triad 1,b3,5
Minor 7th 1,b3,5,b7
Dominant 7th is 1,3,5b7
these are the basic chords you need to know to get started. So........if you have learned a D major scale then you will know that D Major is DEF#GABC#D
If you put a number under all those notes........
DMaj Triad would be DF#A
DMaj7 DF#AC#
D Minor Triad DFA (you flat the F# to make it a F)
D-7 DFAC (Flat the F# and C# to become F and C)
D7 DF#AC (flat the 7th C# to become C)
Every chord relates back to it's major scale if you learn it that way. The major scales is the first thing I have my young students memorize. It makes chord mastery that much easier.