Open your Digital Audio Workstation of choice. A Digital Audio Workstation (DAW) is a program that can do audio editing. An example of a DAW would be Ableton Live 8 or Propellerhead Reason 4.
If you are using Ableton Live 8, select the "drum rack" module in Live's Device Browser on the left side and then drag it into an empty track. If you are using Reason 4, drag the Redrum drum computer from the tool window located on the right side of your screen to an empty portion of your rack.
Drag and drop samples into the empty clips in your drum module.
Open up the sequencer. If you are using Ableton Live 8, double click an empty clip. If you are using Reason 4, click the "Switch to Edit Mode" button on the top left corner.
Select your drum track with the samples loaded in. Use the pencil tool to draw in where each sample will play in the sequencer. The sequencer behaves linearly in a left-to-right fashion. The master tempo controls how fast or slow you want your song to be. In Ableton Live 8, you can adjust the master tempo from the top left corner. In Reason 4, you can adjust the master tempo from the bottom left corner.
Press "Play" and listen to your drum beat. In most DAWs, you can edit your samples or beats while the beat is playing.