Last FNM someone said that when I was attacking, he blocked, then I used regenerate, that his creature didn't take damage. I was under the impression that it created a shield until the next source of lethal damage, but was stupid and didn't call a judge over and just let him have is way. Would my creature still have killed his through combat? Or does the mana regeneration ability immediately take it out of combat?
You are correct in that regenerate creates a shield that is "used up" the next time the creature would be destroyed. When the creature does regenerate, it is removed from combat. However, if you are doing this during combat, and there isn't anything like first strike or double strike on the opponent's creature, both creatures would deal damage at the same time.
So your creature would be dealt damage at the same time your creature would deal damage to your opponent's. Yours would regenerate and be removed from combat at that time, but it has already dealt its damage by that point. Removing it from combat doesn't undo the damage already dealt.
So your creature would be dealt damage at the same time your creature would deal damage to your opponent's. Yours would regenerate and be removed from combat at that time, but it has already dealt its damage by that point. Removing it from combat doesn't undo the damage already dealt.