Open your preferred digital audio workstation, for example Pro Tools or Logic. Depending on your preference settings, the workstation either opens a blank session or the most recently saved session. To get to a blank session from a work-in-progress, open the file menu and select "Open New," "New" or "New Session," depending on the program.
Open a MIDI channel. MIDI, which stands for "musical instrument digital interface," enables you to create a series of notes using data commands, rather than raw audio. This approach is flexible and intuitive. You can alter the pitch, tone and timbre characteristics of a MIDI sequence after recording. Typically, a digital audio workstation has a tab for opening a new channel. For example, Logic has a "+" tab at the top of the channel strip. Click the tab and select "MIDI" when prompted. If you can not see a tab, open the channel from the "File" menu.
Open your workstation step sequencer tool. A step sequencer is a visual grid interface for composing music. The vertical axis represents notes and the horizontal axis represents beats and measures. The step sequencer is typically accessed via the "Tools" or "Instruments" menu.
Open the "Media" menu. Select "Import" and browse for the drum sample files. The samples may be arranged as individual drums, or as a full kit. In the case of the former, import each individually. In the case of the latter, import it in one step. The kit is assigned to the step sequencer automatically. Each drum is assigned a note value in the step sequencer, meaning you trigger each sound from a different row on the grid.
Hit "Play" so you can hear your sequence in real time as you build it.
Plot the fill. Click on different parts of the grid to assign drum strokes to specific parts of the beat. The resultant note is called a "MIDI event." For example, click on the "Snare" row on the final three squares in measure four to create a standard triplet fill. Experiment with placement and drum choice, but keep in mind what is natural to a human drummer. For example, tom fills typically go high to low as the highest tom is next to the snare.
Click on each MIDI event to edit it. Drag down the "Velocity" indicator to lower the volume. A human drummer could not realistically strike a drum three times at exactly the same volume. Emulate human feel by varying the velocity.