Conversion rate would be the rate at which your visitors (or clicks for PPC marketing) turn into sales. For example, 1 sale per 100 clicks would be a conversion rate of 1%.
EPC - is earnings per click.
The AWin index is a little more complex. If you are a beginner, you don't need to worry about it, but it takes into account things like your conversion rate, earning per click, approval rate, and other metrics to help compare one campaign to another.
A great site to learn the basics of affiliate marketing is Wealthy Affiliate. I have been a member there over a year and a half and it has greatly improved my marketing efforts.
