let's say a monster has a AC of 10 and i roll the die and i have a 10 including my atack bonus etc...
does this means the monster gets the hit or did he block it?
If you equal or exceed the AC you hit. So in this case you hit him. From the rulebook:
"Making an Attack
For each enemy a Hero’s power or a Monster’s attack targets,
roll the die and add the power’s Attack Bonus.
If the result of the die roll plus the bonus is equal to or greater
than the target’s Armor Class, the attack hits."