Charging: The action mith took is called Charging. When charging, you can move up to double your speed and still attack, as long as you are moving in a straight, unobstructed line, and you are moving more than 10 ft. By doing this, you build up speed, and can do better on your attack. When charging, you get a +2 bonus to your attack roll. When charging, you must end your movement in the nearest possible square to your starting point that you could attack from. If something blocks this square, such as a tree, or one of your allies, you cannot charge.
Natural 20: When you roll 1d20, and the number on the dice shows 20, thats a Natural 20. Natural 20's are awesome, and everyone loves them. if you get a Natural 20 on an attack roll, that means you automatically hit. No matter what, you hit. If you get a Natural 20 on a Saving Throw, you automatically succeed on your save. Its called natural just to distinguish between rolling an 18 with a modifier of +2, for a total of 20, and rolling a real 20, no matter what the modifier is.
Critial Hits: Ashina almost scored a critical hit! Each weapon has a box for Criticals. Usually they say x2, x3, or 19-20/x2. Thats confusing, but its a really good thing. When you score a critical hit, you hit your enemy in a vital organ or a sensitive area. when a weapon says x2 or x3, you need to roll a Natural 20 to threaten a critical hit. If your weapon shows 19-20/x2, then you threaten a critical hit on a natural 20 or a natural 19. Once you are threatening a critical, you must confirm the critical. To do this, make another attack roll, at the same modifier. If this second attack is good enough to hit, you have scored a critical hit. When you score a critical hit, you do extra damage. If your weapon does 1d6+2 damage normally, and it shows a critical of x2, or 19-20/x2, then you do double damage. You can roll another 1d6+2 and add that to your original damage. if your weapon shows x3, then you do triple damage, and you can roll another 1d6+2 and then another 1d6+2, and add both of those to your original damage. Everyone loves getting Criticals.