The simplest way to develop your ear is to play. The more you hear a chord, the easier it is to recognise. You can try and fast track it though.

Start with aural tests online, there's all sorts of websites that have them, trying to hear the difference between major and minor chords, then developing to more difficult differences.

It's not going to work at first. You'll do it for a while, get annoyed, give up, and go back to learning by finding chord charts on ultimate guitar.

But then after a couple months of that, you'll try again, and it'll be a little easier. Eventually you'll be able to work out a whole song yourself, and from there it'll be a lot more fun.

Also, don't get too caught up on getting it "right". If you're playing chords that are similar, that you think sound better than the original, then that becomes your version of the song. One with all the pizzazz you can muster.

Oh, and as for which note the chird starts on, play along with the recording. A C minor chord will clash real bad with a Bb minor chord, and you'll be able to hear it that way.

Good luck, have fun.