Explicit enhancement points are basically hooks already coded into the program by SAP at various points of the code.
See program RIAUFMVK for examples of these! These are very easy to implement simply go into enhancement mode of SE80
and then create or maintain them as you wish. See instruction below for specific steps required for you to be able to change or create
an SAP explicit enhancement point.
Change an explicit enhancement point
First right click on the enhancement point you want change and choose 'Enhancement Implementation->Change'
Next select the enhancement point and press the green tick
SE80 will now show your enhancement points as editable within the ABAP code so you can change the code as you want.
Create an explicit enhancement point
First right click on the enhancement point where you want to add your code and choose 'Enhancement Implementation->Create'
Next click on the create button and Give it a name, description and assign it to a change request (should not be a Z package) and then simply add the code as normal.
Enhancement transactions
Once an enhancement has been created you can access it again using the above procedure or via
the SAP enhancements transactions SE20 or SE80
If you can't find one of these enhancements where you need it you could also
check out Implicit Enhancement points, which can be implemented
in many more locations.