const vs. let

In JavaScript, There are three ways of declaring a variable, why though? How are they different? const cannot be redeclared. therefore it will have one constant value, and can't be changed. For Example-

const number = 1

number = 2
//Gives an error (const cannot be redefined.)

Whereas let can be changed anytime. For example-

let num = 2

num = 5

//Value changes to 5 with no errors.

Thanks for reading.
Hope I helped :D