RPGMemes

So the d&d rules are fairly vast and can't be summed up all here but, the tl;dr of it:

Every attacking spell or attacking action has an associated mechanism for whether it hits or deals it's damage. Loosely, it's always one of these 3:

• You roll (a) dice, you need to beat bad guy's static number to hit them

• You have a static number, bad guy needs to roll (a) dice and beat your static number to avoid or reduce the damage

• You hit unless they specifically have an ability that makes this not the case

So, for example, "I make a melee attack with my sword against the bad guy" The bad guy has a static number of 17, I roll a (total of) 18 - it hits! Now different dice are rolled to determine damage dealt, based on the weapon.

Or

"I use magic missile on the bad guy" This spell just always hits, that's kind of its shtick. So it hits and I roll for damage, unless they counter it somehow

Or

"I use fireball on this bad guy" My static number is a total of 17, bad guy rolls a 23 - he is still hit by the fireball but will take half the damage (rounded down) when we roll for damage dealt.

Hope this helps!