Bicycle Tutor

I saw the shifting tutorial already and now that makes more sense to me, I'm really new to cycling. My old bike was a mtb. and had 2 levers on each side, one to shift up and then one to shift down along with the gear #. Now I just bought a Giant OCR 3 it has one little lever for shifting. How do I know if i'm shifting up or down when I press it? And how do I fix it/what does it mean when I shift my bike starts clicking like its in the wrong gear?

   

I can't see the lever too much for the glare of the picture. But FWIW, I looked up the specs on the Giant OCR3, and found it to use the Shimano 2200 series shifter.

Can't see in the pic which one of the four it might be, but for what it appears, it's an STI lever, and this might be useful to you.