well, you are in the right place - on the dropdown list over in the inspector where it gives you list of choices for output devices for the midi tracks. On that list you should see any drum maps that you have (which is probably none right now) and the option to add new drum map. You can add one from the list there that has the midi specs for a number of different things.
The basic idea is real-time transformation - midi comes in from a source like a midi keybd or v-drums, and is sent out to the drum map, which maps the incoming midi notes to potentially different notes and also gives you the option to change other things en masse such as velocity - on a per note basis.
Here is the part where it gets, well, less than intuitive - the drum map is not just a way of mapping notes, but also a virtual midi port that once added to the project, becomes a potential midi input for other tracks. Typically they are synths or other midi driven instruments, but can be any midi track.
So you either choose one that relates to the gear or synth you are using, which you can edit with the drum map manager if you need to change it (where it says 'drum map manager', in that same dropdown), or you can just go straight to the manager and create a new one that you can reuse later. You can also save presets that you changed under the same or different names.
With keyboard midi, this is not as useful as with drums, hence the name drum maps, though there is nothing about it that is really limited to drums. That;s just where it's useful. I use it for two things - one is to change, or map,the note that a particular drum pad or v-drum component sends in to match what a softsynth like session drummer or battery might be expecting to make that particular drum sound, the other is to get rid of the notes and associated kit pieces that my pads or kit can never make, or that I never play, this makes it a lot cleaner to work in piano roll because you have things with the right names and you don;t have all the extraneous stuff to paw throug, rather only your particular kit pieces that you plan to use.
Hope this helps. Drum maps, once I got them down, became one of my favorite things in Sonar. They could use to rewrite it as a generic transformation tool, IMO, but what it does is very useful.