Purchase a digital audio workstation (DAW) for your computer. DAWs are computer programs that allow you to record/edit audio and midi tracks. Some of the more well-known DAWs include ProTools, Logic, Cubase, Digital Performer and Sonar.
Obtain a midi controller. Midi controllers are keyboards that transmit midi tracks, also known as musical information, to your DAW. These tracks may include notes, note lengths, velocities (how hard a key is hit) and expression controls.
Purchase an audio interface. Audio interfaces allow you to hear the midi tracks while you are recording them to your DAW. Some DAWs, such as ProTools, require you buy an audio interface to use their program.
Use sampler instrument plug-ins from your DAW that allow you to assign drum samples to different keys on your midi controller. The most popular instrument plug-ins used for R & B beats are Native Instrument's battery and EXS 24, which is found in the Logic DAW.
Find snare drum and kick drum samples that sound good together. Music samples can be downloaded or purchased from various websites, such as Freesound.org. Experiment with different rhythmic patterns until you find the right beat and tempo for your song.
Record the song you created on the midi controller into the DAW. Every DAW has a quantization feature that will adjust your beat by placing into a grid that is based on the measurement and tempo you want for your R & B song.