Is it that feats are actions that can only be used if you have that feat, while with skills you can make a skill check for any skill? Do skills have a more generalized use than feats? Can you not add proficiency bonuses to feats? Do feats not use ability checks? What is the difference?

Are most feats even necessary? Don't abilities and certain class features offer the same uses as feats and more.

Feats are special abilities, you can choose to get one at level 4 instead of an ability score improvement. They are very specific but are generally bonuses or a power up to an already existing ability. They normally don’t take a roll.
Skills are somethings you might be proficient in, ( add the bonus when you make a roll ) such as : if you’re trying to sneak into a castle, you roll 1d20 + dexterity modifier + ( if you are proficient in stealth ) your proficiency bonus. Skills are like specialized ability checks that some races / classes / backgrounds might have a bonus in.

Please correct me if I’m wrong on this.

Quote from Sergeant_Garlic >>

Feats are special abilities, you can choose to get one at level 4 instead of an ability score improvement. They are very specific but are generally bonuses or a power up to an already existing ability. They normally don’t take a roll.
Skills are somethings you might be proficient in, ( add the bonus when you make a roll ) such as : if you’re trying to sneak into a castle, you roll 1d20 + dexterity modifier + ( if you are proficient in stealth ) your proficiency bonus. Skills are like specialized ability checks that some races / classes / backgrounds might have a bonus in.

Please correct me if I’m wrong on this.

 

 If you can override making skill checks by using a feat, then it breaks a core gameplay element

Every player character has the same base abilities, though depending on their build (their ability scores - CON, DEX, WIS, etc; their race, their class, their background) they'll be better at some skills than others, and possibly stink at some. But everyone has those skills on their sheet.

Feats are optional - you can play the game without using them at all. They do a variety of things, like give you extra languages or skills, an ability or spell or attack. But you pick the feat, and not everyone will pick the same feat, and many feats are limited in who can apply them (some are restricted to certain races, or you need a certain Strength score, etc).

So as a sorcerer who grew up on a farm, you're skilled in Arcana, and Persuasion, and Animal Handling (and probably other stuff). But you're not very strong, and you want to up your sorcerer's HP - you take the Tough feat, which increases their HP by two for every level. Suddenly you have 16 (eventually 40, since it keeps going) extra hit points. If you weren't using feats, you could have done that, but it would have taken twice as long (by upping your Constitution score). Or you want a few extra spells -- well, you can take Magic Initiate and pick up some Bard spells and Cantrips. Or your sorcerer is a Tiefling, and you can give them a couple other damage immunities, so they get hurt less. Or yeah, you can use a feat and add double your proficiency to Arcana - take that, wizard who didn't take a feat.

Quote from pocketmouse >>

Every player character has the same base abilities, though depending on their build (their ability scores - CON, DEX, WIS, etc; their race, their class, their background) they'll be better at some skills than others, and possibly stink at some. But everyone has those skills on their sheet.

Feats are optional - you can play the game without using them at all. They do a variety of things, like give you extra languages or skills, an ability or spell or attack. But you pick the feat, and not everyone will pick the same feat, and many feats are limited in who can apply them (some are restricted to certain races, or you need a certain Strength score, etc).

So as a sorcerer who grew up on a farm, you're skilled in Arcana, and Persuasion, and Animal Handling (and probably other stuff). But you're not very strong, and you want to up your sorcerer's HP - you take the Tough feat, which increases their HP by two for every level. Suddenly you have 16 (eventually 40, since it keeps going) extra hit points. If you weren't using feats, you could have done that, but it would have taken twice as long (by upping your Constitution score). Or you want a few extra spells -- well, you can take Magic Initiate and pick up some Bard spells and Cantrips. Or your sorcerer is a Tiefling, and you can give them a couple other damage immunities, so they get hurt less. Or yeah, you can use a feat and add double your proficiency to Arcana - take that, wizard who didn't take a feat.

 Thank you for the info, it was insightful : )

Everybody can use every skill, from the start, no exceptions. You don't have to go out of your way to be able to - you're just better at those you're proficient in. They are your ability to do something. Your ability to do some things might be very poor, for others it might be strong, but you always have some ability. 
Feats on the other hand are qualities you have to acquire before you can benefit from them. They're qualities you by default do not have, and with few exceptions characters start out without any feats.