The big number from the Standard Array (or that you rolled for) is your Ability Score. Your Ability Score determines your stat's Modifier. For the purposes of all rolls in combat and exploration, your stat's Modifier is going to be the most important thing. You add that number to other rolls you make. The better your score, the better your modifier. The bigger your roll against a Difficulty Check (DC) the better you do.
As you can see from the last chart, a traditional part of Dungeons & Dragons design is that certain player character races get increases to certain stats. Elves get a +1 to intelligence, Half Orcs get a +2 to strength, etc. Some modern players and designers feel as though this design choice emphasizes biological essentialism and limits player agency. I do not agree with them but I do like the design choice made to fix it: +2, +1. Simply take +2 one stat and +1 to another. So if want to be a Half Orc with a focus on intelligence over strength, you aren't limited by your built in modifiers. If you would like to build your character out this way just let me know in advance.
Zuberi is a Fighter. He has a Strength of 18, a Dexterity of 15, a Constitution of 12, Intelligence of 8, Wisdom 12 & Charisma of 11.
If you compare Zuberi's Strength Score to the chart above, you will see that having a score of 18 gives him a Modifier of +4. His low Intelligence score means that he has a negative modifier, -1. Lets get into how that works in play.
Zuberi needs to leap over a chasm, it's the only thing standing between him and the entrance to a dungeon full of loot. The Difficulty Check is 12. Zuberi makes a strength test to attempt his leap. He rolls a d20 and the result is a 10. But because he adds his strength modifier that brings him to a 14. He easily clears the distance.
Every character class also has a Profiency Bonus. This is a number between 2-6 that changes as you level up. All characters begin with a +2 Proficiency Bonus. You add this number to rolls made for skills you have Proficiency in. Every class has a bundle of skills they can select to gain proficiencies. Fighters can select 2 skills from Acrobatics, Animal Handling, Athletics, History, Insight, Intimidation, Perception, and Survival.
Because Zuberi selected Athletics as a Proficency, he could test his Athletics skill as a way to leap over the chasm. Because his Proficiency Bonus is +3, he would add that to his modifier, giving him a bonus of 7 to his roll.
On the flip side, Because Zuberi has a low Intelligence Score of 8, his modifier is -1. He also has no profiencies in Intelligence related skills. If Zuberi was asked to make an Investigation roll of DC 10 to look for traps and he rolled a 10, his modifier would bring his roll down to a 9. He would not notice the pit trap straight ahead of him. He might die if he falls into it. But don't worry! You have teammates with different stats than you to hopefully help avoid death.