There are built-in GML functions that operate on either an object handle or an instance handle, depending on the function.
Functions that only take an object handle usually return information on all of its instances, such as instance_number, on the object itself, such as object_get_name, and on one particular instance of the object, such as instance_nearest and instance_create_layer (in this case, creating a new one). Another example is the function instance_change which operates on the current instance and changes it to use a different object (and hence use its events).
-Functions that only operate on instances mostly do so without arguments, as they operate on the instance executing the code. For example, instance_change as previously mentioned, instance_copy, motion_add and various other functions will operate on the current instance. There are functions that operate on instances via arguments, but they also accept object handles and are covered below under Mixed Functions.
+Functions that only operate on instances mostly do so without arguments, as they operate on the instance executing the code. For example, instance_change as previously mentioned, instance_copy, motion_add and various other functions will operate on the current instance. There are functions that operate on instances via arguments, but they also accept object handles and are covered in the next section.
There are built-in GML functions that take both an instance handle and an object handle.
The difference in most use cases is simple: passing an instance handle only modifies that one instance, and passing an object handle modifies all instances of the given object.