Connect the MIDI interface to the appropriate port on your PC. Some MIDI interfaces are designed for USB (indicated by a crooked trident symbol) whereas others are designed for FireWire (indicated by a broken letter "Y" symbol). Insert the USB or FireWire connector into the corresponding port on your PC. If your interface is bus-powered (meaning that it requires your computer to power it, rather than an electrical outlet), make sure to connect it to a port directly on your PC and not to an external hub, which typically contains less power and may prove insufficient.
Observe the two round MIDI connectors on the opposing side of your interface. One connector should read "MIDI In" or "To MIDI In," and the other should read "MIDI Out" or "To MIDI Out." Some interfaces use different colored connectors to differentiate between "In" and "Out."
Insert the "Out" connector into the corresponding "MIDI Out" jack on the back of a MIDI keyboard, in order to send MIDI notes from the keyboard to your computer. This connection will enable you to play notes on a keyboard and simultaneously play sound through your PC, using digital audio software.
Insert the "In" connector into the corresponding "MIDI In" jack on a MIDI sound module or other digital sound generating device if you wish to transmit MIDI from your computer to an external component. For example, if you connect your PC to a sound module using "MIDI In," you can play a note sequence on your computer and transmit it through the sound module speakers, using the sound settings of the external device.
Open a digital audio program on your PC. Not all audio editing programs can interpret MIDI notation, but many professional and free options exist. Consider using a professional audio production program such as Pro Tools, Logic or Cubase, or a free MIDI editor like QTractor, Rosegarden or LMMS.
Create a MIDI sequencing track. In recording terminology, a "track" simply refers to a layer of recording (like guitar, vocals, bass and drums). It will appear on your screen as a horizontal bar, on which you can record or sequence music. To enable MIDI sequencing, locate the "New Track" option on your menu bar and select the "MIDI Track" or "Virtual Track" option. It may also appear as "Software Track" in some programs.
Begin transmitting MIDI through your interface. Most interfaces do not require the installation of software drivers, but if your interface included a CD-ROM, install the driver before proceeding. When everything is ready to go, transmit MIDI according to your connections. For example, if you connected a keyboard via "MIDI Out," begin playing the keyboard to transmit the music notes to your PC. If you connected a sound-generating device via "MIDI In," begin sequencing notes on your PC to transmit sound to the module. To sequence notes, use your connected MIDI keyboard or open your software's "Piano Roll" or "Sequencer" window to insert notes manually, using your mouse.