Hi man, as some of the other guys have said before, ther are kind of rues to harmony and music in gen but rules are ther to be broken and especially in music, to make a chord you have a scale as said before c d e f g a b etc these are called intervals c to d is a major 2nd c to e a major 3rd c to f a perfect 4th and so on google it to get a better understanding of ther relationships, ( as they tend to want to resolve to some place this needs time by you to investigate to understand and be able to use )you make chords out of said scale by stacking notes on top of each other ie c-e-g makes a c major chord as a simple triad but you can add more notes on top of them three too to make it more fuller, exciting/colour or moody/flavour or what ever you want to call it many diff people have many diff ways of describing this, so again the way you make a chord is take a note miss the next one then take the one after that and stack them ( take C miss D take E miss F take G miss A take B this will give you C major 7 and the more you add the bigger the chord, if sounding to full or mad for your ears you can start to omit some notes ie the root of the chord and the 5th of the chord as your bass will prob be playing the root but you gotta leave your 3rd in ther to determine the chord type ie major, minor, so with all that said this is how you would go about creating your harmonies too, you can flesh out using this method some parts and then use your ear to get from one line to another, and just as ther are only 12 notes in all chromatic wise to choose from its the rhythm and style/genre that creates colour/flavour to your music so get to grips with some simple block ooooos and aahhs first of all then maybe try some counter melodies in your music maybe just one running along side your verse vocal after you get to grips with those try and get more experimental and add some from diff styles of music ie have a listen to some country music and try and recreate ther style and weave it into your song(s) o maybe some gospel and doo-wop, just some food for thought but like I said all diff styles give diff flavours and adding these to your own tunes can be real fun and surprising as well as rewarding, if you listen to the Beatles they have a lot of early black USA bands harmonies in ther songs but with them singing them and against the song it sounds really good and not to obvious until you listen closely and dig around into maybe what they would have been listening to all those years ago, but you need to get to grips with chord construction first of all its a simple thing but really helps with all things musical as far as harmonies and arrangements go, I hope I haven't cabbages your head just trying to help
