Connect the instrument or microphone to the computer's audio interface using a 1/4-inch or microphone cable. You can plug directly in to the "Line In" jack on many computers with a 1/8-inch adapter. If the audio input signal is relatively low, you will need to use a preamp. If your audio interface does not come with a built-in preamp, you will need to connect the signal to the preamp first, and then to the interface or computer.
Connect your audio interface to your computer's USB port. Most audio interfaces come with the appropriate USB cable, and some even have it pre-attached. Although USB-powered interfaces are common, some require an external power source. Make sure your computer detects the interface (an indication should pop up). Some interfaces will require the installation of drivers in order to function smoothly.
Open your computer's audio recording software. Many programs are available to download for free, and some even come standard with certain computers.
Start a new project in your software.
Check the levels of your audio signal. Make sure the incoming signal does not peak, clip, or distort. Your audio recording software will have an indicator that shows signal peaking next to the level meters. Lower the audio input level if the signal peaks.
Click the record button on your software. The computer will now record any incoming audio signal.