The answer to that would be subjective. Genshin Impact’s combat system rellies on having up to 4 characters in your party that you change on the fly (you can only have 1 character playable, other 3 are off-screen but you can shift to them on the fly, as in in the middle of your combos). The game has a lot of characters and they have different elemental abilities. The main purpose of the combat system is to make a party of different elements and use them in the middle of a fight (or a combo) to create elemental reactions.
For a more beginner friendly explanation and to see this in action, you can check out this video: