What are custom functions?
Custom functions are functions which you have made yourself. They can be Private (only the class in which it is created can use it) or Public (any class may use it). They are able to take parameters/arguments, can return data and can be ran on separate threads.
When should you use custom functions?
Whenever you have a script which needs to be ran over and over again at different positions within your source code you should create one function to contain the script. This way, you can call the function every-time the script needs to be ran, this saves time and