This is a very simple script for GMS2 users who came from GMS1, and are used to the GML function named instance_create().
In GMS2, due to the introduction of Layers, instance_create() was replaced by two functions: instance_create_layer(), and instance_create_depth() for backward compatibility.
This script simply wraps both of those, checks to see what data type the third argument is, and then passes the arguments into the correct function. If argument is a string, instance_create_layer(), otherwise instance_create_depth().
This is a pretty pointless script, but if you enjoy having a function called instance_create() available to your projects, and can't stop typing it, then this asset is for you!