Open your preferred music software program. Double click the desktop icon or open the program from the "Start" menu. If using a Mac, you can open the program from the desktop or "Applications" folder.
Disconnect your external MIDI controller, if necessary. Remove the connected Firewire or USB cable from the port on the side of your computer. Music software programs are typically configured to automatically recognize USB or Firewire connected devices and assign them as the default MIDI controller. If such a device is connected, it will be the default device until you disconnect it.
Access the input devices menu. Input devices are the default hardware items that you use to send audio and MIDI to your computer. The location of this menu differs from program to program, but is typically located under "Tools," "Devices" or "Audio."
Select "Computer Keyboard" from the input devices menu to assign the computer keys as MIDI controllers. The process for "musical typing" is slightly different if you're using Apple's Garage Band program. All you need to do is click "Window" and select "Musical Typing." There is no need to access the input devices menu.
Access the instruments menu and select your preferred source sound. The "Instruments" menu is typically located on the top of the program interface. In some programs it is located under a sub menu. For example, in the Logic program, click "Media," then select instruments.
Type a melody. Now that they keyboard is assigned as the MIDI controller, each key controls a different note or command. For example, in Logic keys "1" and "2" trigger a pitch bend. Familiarize yourself with the layout of the sounds across the computer keyboard. Musical typing keyboards are typically laid out intuitively, with the high notes on the top row of keys and low notes on the bottom. Pitch increases from left to right.