Drum maps are very, very useful things.
What they do is look at an incoming MIDI note and turn it into another. So if, for example, the MIDI controller sends note 60 on channel 1 to MIDI port 2 a drum map can be used to convert that into e.g. note 36 on channel 10, MIDI port 3. Software synths/sampler inputs are MIDI ports in the same way hardware MIDI kit is.
The best way to find how they work is to create one yourself. The first one or two are likely to take a bit of time, bit once understood they are pretty straightforward and can be useful any time you need to reassign MIDI notes "on the fly". An example of why this is useful outside just drums is that what some systems/synths call C1 others call C0 which means their notes disagree by an octave unless corrected in either direction so they end up the same. Roland and Yamaha back when MIDI was new can be blamed for the two different octave numbering systems if I remember correctly. Similarly, some companies number MIDI notes and continuous controller data 0-127 and others 1-128.
Trying to get a MIDI controller to work and route its output to where you want it really does mean getting your head around some MIDI basics though - note numbers and messages, channels and ports in particular. Otherwise you're mostly guessing and hoping to hit on something that works by chance.
And you may find the same sort of problem with a commercially built MIDI kit or controller, but at least they are usually fairly well documented.