The best nudge is that this is a word-based version of the classic numbers game Mastermind. There are many free ways to play Mastermind online. Simply Google 'play mastermind online' and pick an option. Once you get good at that, this puzzle will fall right into place for you.
The answer is a six letter word, given in the Spoiler below. DO NOT CLICK THE SPOILER BUTTON IF YOU DON'T WANT TO SEE THE ANSWER YET!