View FM Documentation

It is a simple process to retrieve the SAP function module documentation available within your SAP system and can be done via SAP transactions SE80 or SE37.

Step 1 – Execute transaction SE37

First, execute sap transaction SE37 and enter the function module name. Then press the display button
trasnaction se37

Alternatively, choose menu option Goto->Documentation->Function Module Documentation. The only problem I find with this option is that the documentation popup box appears underneath the current SAP window so you don’t actually see it without moving the window

SAP function module documentation 

Step 2 – Display Function Module documentation

If you selected display you will be taken to the FM details, now simply choose the menu option goto->Documentation. 

The FM documentation will now be displayed
SAP FM documentation

Step 3 – Alternate way to display documentation for an FM using transaction SE80 

You also get the same options to view FM documentation within SAP transaction SE80
SE80 FM documentation options