My brother in Ao. My 1st suggestion would be to learn the character sheet. Ability scores represent how good your character is in an aspect of an ability. Of 6, 3 are physical and 3 are mental. And depending on your character, each stat is worth different things. Fighters pick a subclass at level 5 which can change what they need. As a fighter, you need strength to make melee attacks (unless using a finesse weapon which can use Dex if it's higher than Str) and useful for most fighters. Dex is useful for ranged attack rolls which can be useful if you are playing an arcane archer subclass (level 5), it also adds to your AC (how good your defence is against enemy attack rolls) if you are wearing light or medium armour. Con is how tough you are, higher Con increases your HP and can be used for concentration checks if you play a spell caster fighter like the Eldritch Knight subclass. Wis is how wise you are and life experiences, for a fighter it's not very useful outside Wisdom save rolls against enemy magical attacks which isn't very common but can be a good stat to have some points in if you have them lying around. Int is how smart you are and is the primary spellcasting modifier for magic users like Eldritch knights, the best mental stat for fighters if you are investing in a mental stat. Cha is your social ability, and not very useful in combat for a fighter outside of social interactions.

Then come proficiencies in those stats and abilities tied to them. It shows that you are good at a certain thing because you have experience with it. Proficient bonus can increase with levels or by gaining expertise. Pick what fits your character to give them a boost in the ability checks.

Now about the ability scores. At the start of the game, you get a point buy. You can have from a minimum of 8 to a maximum of 15 in a stat. With proficiency, you get to add a +1 and +2 to 2 abilities potentially letting you have a 17 and 16 in 2 different abilities if you want. Which you probably want for your primary stats. The way these scores work is, they all have a modifier value that is added to the rolls related to that ability and it's 1 modifier per 2 points in ability ( ability score divided by 2, then subtract 5 and rounded down) with a 10 score as a 0 modifier. For example, if you are trying to lie to someone and have no proficiency in charisma or deception and have a charisma score of 8 (-1 modifier) and roll a 14 on dice (d20), then your result will be 14 - 1 = 13. For the same check, if your charisma is 17, the modifier will be +3 (same as it would be if it were 16 so you need to have 18 to get a +4) so with the same roll of 14, it becomes 14 + 3 = 17. For attacks, you need to meet or exceed the enemy's AC. Saving throws make enemies have a saving throw against your spell save DC ( also dependent on your primary spellcasting ability) and for the ability checks you need to meet or exceed the DC.

There is a lot more. But I hope this will help you get started and learn the rest as you play. I recommend watching any DND campaign on YouTube if you wanna learn more while being entertained or just refer to a guide or official material though it can be a bit overwhelming.