In Path of Exile, I was reading about ppl farming equip or sword with lvl 10 and were able to level with all that items to level 70 and much further. How does the item level design work? How does it all work? 

1. Higher level doesn't necessarily mean better. There are items you can get early and scale late into the game (like Tabula, which gives no stats but give you a 6-link for a HUGE damage boost). Max links is a function of max sockets; you can get six-socket items at ilvl 60 50. You can also choose poe buy items.

2. You never need to "reforge" anything, although there are some uniques you can upgrade via a prophecy (or more likely just buy the upgrade from another player).

3. Generally, it's best to level by scaling life and elemental resists as your main defenses and not worry about base stats until you get to endgame. Higher item levels mean higher stat values can roll, so you want to be on the lookout for upgrades as you go.

4. If you're levelling an attack-based build, you want to use the best unique weapon of the appropriate weapon type for your build that you can currently equip. They're usually cheap at this point in a league. If you're levelling a spell build, Tabula is pretty great as are items that give your skill gems more levels (links and gem levels give you most of your damage scaling for spells).

5. Find yellow items of the right bases and ID them. Hope for good stats you need. Try find one's with links already or 4 sockets so you don't have to burn jewellers/fusings on them too. Plenty drops so just keep checking them. You can vendor armourer scraps for scrolls if you keep running low.

I believe that other experienced players will be better than my tips, but these are the reasons for my success, and I sincerely hope it will help you too. Finally, don't forget that U4gm.com Sale Cheap POE Currency, POE Orbs, POE Items.