What a can of worms you opened!
At the beginning, as I assume you are, you're probably ok with just using the aggregate stats at the bottom. These aggregate stats should give you a rough idea of how much better or worse each piece of equipment will make you, but this is mainly an estimate. If a weapon gives you +20% damage output, you should strongly consider it. If it only gives you +2%, are you giving up anything else for that measly 2%? And although healing is always nice, early on it's really weak, and generally should be ignored. You should be fine with potions.
Things to take note of: What class are you? Each class has a primary stat (strength, dexterity or intelligence) that is used for their attack strength (WD and Wizard - int, Barb and Crusader - str, DH and Monk - dex). You can safely ignore the other 2 stats, but luckily the drops you get will focus mostly on your primary stat (and vitality). Between that primary stat and vitality, those are the primary stats you'll want to increase, and most "magic" weapons you get will enhance one or both of those stats.
After those, there are a ton of other stat enhancements that you may or may not care about on that class or character, like attack speed (looks great on paper, but not as well in practice), heal on hit, heal on kill, HP regen, resource regen, +XP on kill, +gold, +damage on skill X, etc. You'll get some of these as secondary enhancements after focusing on the primary stats, and you'll see which ones help you when.
One stat I do focus on early is +run speed. It only appears on boots (go figure), and although the bonus is minor, I will keep a set of boots with a decent +run speed with marginal other stats over a drastic drop in run speed for anything else, including +damage. It is something you will notice right away and you'll be happy to have it.