Open your preferred DAW; for example, Cubase or Logic. The DAW will function as the interface and storage medium for your samples. You use it to assign specific sounds to specific keys on the external controller or keyboard.
Click "File" and select "New MIDI Track." By opening a MIDI track, as opposed to an audio track, you assign the attached MIDI controller or keyboard as the primary input device. Name the MIDI track "Samples." This way you know which track to engage when you want to use your external controller to trigger samples.
Open the piano roll editor. The piano roll editor emulates the layout of a real piano and lets you manually manipulate the notes with your mouse; for example, you can move a D to make it a D sharp or you can elongate a note by dragging it with your cursor. It offers an intuitive editing interface.
Open the virtual studio technology, or "VST," inspector window. The method for doing so varies slightly according to what program you use, but the VST window is typically located under the "Instruments" menu.
Click "Edit" and select "Create Map." This assigns a new map to the MIDI channel and opens a new mapping interface. The interface has a graphic of the piano roll and each key is vacant. Click "Assign" and select a key from the drop-down menu. The keys are labeled by note and then by octave; for example, "C3" is the C note in the third octave along the keyboard.
Select "External Instrument" from the "Assign" menu and browse for your samples. When you see the sample that you want to assign to the piano roll, click on it. This loads the sample into the instrument library and assigns it to the selected key. Repeat this process for each sample.