i dont get armor class mechanic, why more ac give more dodge ?
AC represent how difficult your enemy is to damage. That protection can come from protective spell, from characters agility, from shield he is carrying and/or armor he is wearing. As such, heavily plated character and dexterious rogue have same ACs, representing different ways in which those characters protects themselves from damage.
It might a bit of missed potential to lend our character builds more variety in gameplay. In Pathfinder, for example some spells are applied by touch, and therefore armor bonus doesn't apply. I also quite like what PoEs did - armors providing damage reduction which slowing character's movement and attack speed.
5e keeps very basic approach to AC - and like a lot of it it is straightforward but it works alright, if lacking in nuance. Still an improvement over D:OS2 armor system.
