Congrats.
You speak of "unusual" chords. I take it you mean those nice juicy ones, like ending on a chord of C major made up of (bass upwards:) C B E G (A) D.
Snazzy chords only come with experience experiment and practice, and playing pieces that use these kind of chords if you can find suitable music.
It's worth learning basic 4 part harmony (grade 6) i) so that you know what you must include and what you may exclude from chords.
ii) to learn about "suspensions" and apoggiatura chords - chords that contain notes alien to the proper harmony (of the chord) but resolve onto harmony notes, or onto new discords (that need further resolution).
{You're okay that's what discord means? A chord that has to be resolved}
iii) to learn to add dissonaces to basic triads - 7ths 9ths 11ths 13ths - and what to do with them!
It helps you to learn what's possible when moving through a sequence of chords....and when you can surprise people by not resolving things as they expect - or ending a sequence unexpectedly - like, imagine getting ready to end in C major but landing on A major instead.
But it's just as important not to take the "rules" of 4-part harmony too seriously - they're there mainly to help musicians develop good musical taste so worth paying lip-service to - but you won't be excommunicated if you break them here and there!!
Why 4-part harmony? It's less restrictive than 2 and 3 and the rules are less strict than 3 part (best to study counterpoint if you're interested in those). But it's restrictive enough to teach you what you can omit and not, when, say, writing for a quartet. But you can write as many notes in a piano/guitar accompaniment as seems right, of course.
And....in your own work there's nothing to stop you breaking into 5- 6- or more parts if you suddenly hit on a super sound! (Just don't do it in the exam!)
Don't be afraid to experiment. Write things down, learn what you've done, what extra notes you can add (and when not to use them). Remember, a single well-chosen dissonance can be magical in effect; just as too many extras might sound thick and horrid - you just have to learn the circumstances when to do what.
Grade 6 is where you become aware of these things (if you want to - you don't have to, you can just follow rules and still pass).
Very best of luck. I go along with finding a teacher if you can afford- even half-an-hour a week may be enough. Later, you may find you can work well on your own.
