I don't understand type annotation

Can you explain to me on what they are used for and some examples

A type annotation is a way to specify the type of a variable or constant by adding a colon followed by the type name after the variable or constant name.

For example, to declare a variable as a string, you can use the following syntax: var message: String = "Hello, World!"
In this example, message is a variable of type String that has been set to the value “Hello, World!”.

Similarly, you can use type annotations to declare a constant as an integer: let numberOfApples: Int = 5