To add to what others are saying, the other type of check that happens in combat is a Saving Throw - spells in particular, the majority of them that cause status effects or deal damage, require an enemy to make a saving throw instead of your character making an attack roll - the spell will always be on target and do its thing and you don't make any roll at all; it's up to the enemy to attempt to resist it. Enemies make saving throws in the same way that you do - they'll roll a d20, and add their modifiers, and if they match or exceed your save DC, they'll pass.
If you're using an ability or spell with a saving throw, rather than an attack roll, it will tell you what type - such as Wisdom or Dexterity; that is the ability that your target will use to make the save and avoid your spell - a spell casting player will always use their casting ability score to deliver the spell and set the save DC, a battlemaster will always use their Strength/Dex to set their save DC, and so on.
The main reason to bring this up is that most damage-dealing spells of 1st level and higher (that is, not your cantrips) will always deal at least some damage, even if the target succeeds on the saving throw - this is almost always half of the damage that would have been dealt if the target had failed the save. With the present game, attack roll spells and abilities have been given a lot of favour - we have enemies with lower ACs (the number attack rolls have to meet or beat) than you might expect, and sometimes higher stats (which leads to them having slightly better saving throws than you'd expect), and lots of new bonuses that add to attack rolls against enemies, but not many that hamper their saving throws; this means that you will see a lot of enemies saving against a lot of your efforts, and taking reduced damage. This is a Larian design oversight currently.
Save DC is also harder to raise, and will increase by less overall over the course of your adventure, than your attack bonus will... while, on the other side, enemy saving throw bonuses climb a lot, and their Ac remains fairly stagnant... this means that in the later stages of the game, you'll be fighting with maybe a +12-14 attack roll bonus, against enemies with 21-22 Ac at most - giving you very good base changes to hit... but those same characters might have, at best, a Save DC of 19-20, while the enemies will have saving throw bonuses of +12-14 or even higher.. making it substantially harder to land saving throw spells. There are reasons for this, and it's not as unbalanced as it looks - but it's something that Larian's design doesn't seem to be bearing in mind for the time being.
