In Pine Script, functions are defined using the function keyword, followed by the function name, and a set of parentheses that may include parameters. The function body is enclosed in curly braces {}.

This example defines a function named myFunction that takes two parameters param1 and param2, and returns the sum of these two parameters. The function is called by passing in the values 5 and 10 as arguments, and the result is stored in the variable result.

You can also define a function without any parameter and without any return value like this:

It's important to give a meaningful name to the function and also to document the function with the help of comments, so that it's easy to understand the purpose of the function and how to use it when reading the code. Additionally, it's a good practice to include error handling in the function to handle any unexpected cases.