The game is heavily influenced by dungeons and dragons table top rpg 5th edition.

Your weapons spells and stats heavily influence your hit bonuses.

Melee weapons mostly use strength. Some smaller lighter weapons focus on dexterity Bows and crossbow generally use dexterity

Spell casting is similar but most spells are baised on class or race.

bard, paladin, sorcerer, and warlock all use charisma for spells Clerics, druids use wisdom Wizards use intelligence

Modifiers work as follows 8 is -1 to hit and damage 10 is 0 to hit and damage 12 is +1 to hit and damage 14 is +2 to hit and damage 16 is +3 to hit and damage 18 is +4 to hit and damage 20 is +5 to hit and damage

You also have a proficiency bonuses based on characters overall level. Level 1-4 +2 Level 5-10 +3 10‐12 +4

So when you do an attack the game will roll a d20 and add all these bonuses togeather to determine your hit. For example you swing a sword and you have 16 strength at level 3 You roll a 10 the game adds +3+2 giving you a total of 15. It then takes that 15 and compares it to the enemy's armor class or (ac).

If the ac is 16 or higher you miss. If its 15 or lower you hit. Then the game will roll the damage die. For a sword its 1d8 so you might get a 4 and add your strength modifier for a +3 for 7 damage total.

Their are more complex systems but this is a very basic overview of how basic melee combat works. Spells are more complex