This question doesn’t have a simple answer, because in Genshin Impact, each character has a different type of power (called “visions” in the game), and everything depends on how you combine these powers into elemental reactions, and the type of enemy you’re facing. I’ll try to explain the mechanics as simply as possible:
The Visions are: electro, pyro, cryo (ice), geo (rock), hydro, dendro (plants) and anemo (air). In this game, you control a team of up to 4 characters, and if, let's say, you attack an enemy with pyro, and then electro, you’ll create an elemental reaction called "overload", which can be effective against ice enemies, for example;
Besides the vision, characters are divided into "qualities": 4 or 5 stars. The former are easier to obtain, while the latter are a bit harder (they cost gacha) and are generally more elaborate and efficient. Examples: Raiden Shogun is a 5-star electro character, while Razor is a 4-star electro character.
Important note: in the beginning you'll be using mostly 4-stars, but it doesn't prevent you from creating powerful elemental reactions;
As for commands, there are three basic attacks: Normal (with weapon), Skill, and Burst. The latter two involve vision-influenced effects (electric strikes, for example).