LoL!
The +0 all the way to +10 is the refining state where +0 is not refined and +10 is refined 10 times sucessfully.
Each weapon has a level, for lvl 1 weapons, each refinement will add +1 to the attack strength. For lvl 2 weapons, each refinement will add +3 to the attack strength. For lvl 3 weapons, each refinement will add +5 to the attack strength. For lvl 4 weapons, each refinement will add +7 to the attack strength. You will not see it in the item description but you can see it in your stats as varik68 said.
Let's say your refine a lvl 2 that has 50 attack strength up to +5, when you equip it, it would appear 50 + 5 in your stats window. The attack strength in the window is base attack + refinement. Your base attack consist of your str, dex, lvl, and base weapon attack.
For armor, each refinement will add +1 to your defence, so let's say you have a full plate with 10 defence refined to +8, your full plate will have a total of 18 defence. Once again, it will not show on your item description but you can see it through your stats window. The defence stat is percentage defence + damage defence. That means if your defence was 50 + 30 then the damage to you will be reduced by 50% and then subtracted by 30. Ex: 100 base dmg on your 50 + 30 defence, 50% of 100 is 50 and subtracted by 30 will give you 20, so the monster or person will deal 20 dmg to you.
