Functions give a name to reusable logic. Parameters bring values in, and return sends one value back.

Return a value

functions.swift
func addBonus(score: Int, bonus: Int) -> Int {
    return score + bonus
}

let score = 
let bonus = 5
let finalScore = addBonus(score: score, bonus: bonus)
print("final=\(finalScore)")
func addBonus(score: Int, bonus: Int) -> Int {
    return score + bonus
}

let score = 
let bonus = 5
let finalScore = addBonus(score: score, bonus: bonus)
print("final=\(finalScore)")
func addBonus(score: Int, bonus: Int) -> Int {
    return score + bonus
}

let score = 
let bonus = 5
let finalScore = addBonus(score: score, bonus: bonus)
print("final=\(finalScore)")
return `return` ends the function call and provides its result.