Now coming to your question. Lets say, you want your application on secured port 443 from Internet and you have your application running on port 799 with no encryption.
In this case, you will need only client SSL profile to be mapped on the virtual server i.e. SSL Offloading. In this case, client request to F5 comes as encrypted. Then F5 decrypts that traffic and send plain traffic to backend pool member.
In any case, if you want to have encrypted traffic on both client-to-F5 as well as F5-Backend_Server, in this case, you would need to have client ssl as well as server ssl profile on the virtual server.
You need to have proper certificates and key configured under SSL profiles.