Initiative determines the order of turns during combat.
When combat starts, every participant makes a Dexterity check to determine their place in the initiative order.
Formula of calculating initiative 5e.
The modifiers include those from classes, races, or other features.
Dexterity measures hand-eye coordination, agility, reflexes, and balance.
Suppose your dexterity modifier is 10, calculate your initiative 5e if no other bonuses were included.
Therefore, your initiative 5e is 10.