There are several different skills that a person can acquire.

Each skill is associated with a different stat. Rolling for a certain skill means rolling a regular d20, and then adding the modifier for the stat it's associated with. For example, if you have a +2 to Intelligence and perform an Investigation check, you're rolling a d20 + 2.

You may select three skills. These three skills will have a +2 bonus to them. So, for example, if Investigation is one of your skills and your Intelligence is already +2, you can get a +4 on all Investigation rolls. Selecting a skill can also soften or get rid of a negative modifier.

One of your three skills will automatically be the skill most associated with your character's talent. If none of the skills match your character's talent, you'll get an unlucky bonus and instead be allowed to pick a fourth skill.

If you have five positive Interact actions with another character, you can gain a +1 to a skill that character has, but you don't.

Strength Skills: Athletics

Dexterity Skills: Acrobatics, Sleight of Hand, Stealth

Intelligence Skills: History, Investigation, Nature, Religion, Arcana. The latter two will rarely be used if ever, I imagine. I might use them for Interact actions depending on what two characters are doing together.

Wisdom Skills: Animal Handling, Insight, Medicine, Perception, Survival.

Charisma Skills: Deception, Intimidation, Performance, Persuasion.