What does this do? Add stats for items? Also still looking for best mm build out there

ye, it add 1 mod to the item...

so use like leg mod everytime?

Depends how much money you want to sink into it. You could get a terrible mod or a good mod regardless of what one you use.

oh is it worth it?

I have only used it like 2 or 3 times and got + to an ele def. Then I went common and the best things that I get are + to a stat. I assume if you use leg it a lot you will get + to stats and it will be a lot but unless you can afford to "gamble" 50k for an item I would say use rare or common. They can give (using my last item as an example) +8 str and some ele def or maybe even life.

its useful in case you find an item with a couple very good mods, but no other mods
you can augment it to fill the number of mods possible, theres 3 tiers of mods you can add, from cheap to very expensive, chance to get better mods are better with the higher property choice you take

hmm, so when agumentin item, what are affecting the mods that u are gonna get? is your character level? item level? or is it totaly random'?

lets say that i have 20lvl guardian and i wishing to get +x shield master and the item im gonna agument has item level of 28 are there any chanses of getting shield master? or does my char need to 25lvl or higher?

you can spawn any skill to my knowledge, but I think your level does come into play. if it could spawn from a drop, then the augamatrix can spawn it.

also, tier 1 could be +1, rare could be +1 or +2, and legendary could be +1 through +3. So spending more does not guarantee better mods, just the chance of one.

These are the skills I use on my MM; http://hellgate.ingame.de/skilltree/marksman/?l=50&s=030770070007050000000300a00