[ivansc]

Hi and welcome to the forums. My best guess is that you havent been recording anything but the actual MIDI from your drums, rather than the audio.
Basically you have two choices - either run the audio out(s) from your kit into whatever you are using for an audio/MIDI interface so you can direct;y record your Kit sounds into a track in reaper, or if you have any drum vsti plugins, put them on the track where you are recording MIDI at present and pipe the MIDI into the virtual instrument.

I am off to bed right now but either someone in a different timezone will step in or I`ll catch up with you tomorrow.
If you DONT have a drum VSTi and want to try that way, download and install the free MTPowerDrums 2, which is now free and pretty decent.
And in the meantime if you didnt already, download the free User Guide and check out the free video tutorials, all at reaper.fm

Have fun!