Q: why do diminished chords and augmented chords sound similar to me?
A: you're probably using them totally outside of a song right now. Try taking a song you already know, and swapping out a 'diminished' chord with an 'augmented' chord and i think you will see that it immediately will sound ruined. But, if you don't think you know any songs with  'diminished' or 'augmented' chords, then i would recommend skipping this topic until it comes up naturally in a song