I'm confused

What do defense and armor do?
Do they make the damage done on you less?
If so, if the combination of armor and shield together make about 20.
Wouldn't it be accurate to say that you could buy 20 defense crystals and not have to wear armor?

I'm confused on what they even do (bot wise).
I know defense, the higher you have the more exp the other person gets
But i've never seen it lower the damage rate, if so by how much?

Armor + Shield add to defense..

Let's say your defense = 0.....

If you're wearing an armor and shield that both = 20, it would be as if your defense = 20

If you bought 20 defense crystals in addition to the armor and shield, it would be as if your defense = 40

Armor/shields are typically cheaper than buying defense crystals.. hence their usefulness for those who arent rich

Thank you so much