🍁Nine Ancient Obelisks

I still don't understand anything about Offensive Units (OU) and Defensive Units (DU). Let's say I have 2 DU and 3 OU. And then...?

Added after 41 seconds
And what does "OU is set at the beginning of the day" mean?

Added after 2 minutes

If a melee weapon has 100 damage, then with 75% Block Chance (BC), the damage dealt by the character will be 75; with 300% BC, the damage will be 300.

But where can I see this "character damage"? I don't see it anywhere.