Hi,
As a starter, please, read this documentation:
http://help.sap.com/saphelp_dimp50/helpdata/en/f0/ca3fd2260211d28a430000e829fbbd/frameset.htm
For activation of additional FM assignment refer to this documentation:
http://help.sap.com/saphelp_dimp50/helpdata/en/61/f2d2642db9e94dbd9c09439babcc72/content.htm
Regards,
Eli