Install the Tascam US-144 driver on your computer. The interface includes an installation CD, but if you misplace it or buy the interface secondhand without a disc, you can download the driver from the Tascam website.
Connect the Tascam US-144 to your PC. The US-144 includes a USB cable with a rectangular connector on one end (USB-A) and a square connector on the opposing end (USB-B). Connect the USB-B side to the back of the Tascam interface and connect the USB-A side to your computer using any USB port.
Open Audacity. Click "Edit," then"Preferences" on your menu bar and select the "Devices" option in the left column of your "Preferences" window. This will take you to the list of preferences specific to external devices.
Click the "Interface" pop-up and select the "Tascam US-144" option. Select the same device on the "Recording" menu. If you want to feed the audio through the Tascam US-144 (using external speakers), select the device on the "Playback" menu as well, otherwise leave the default playback settings. Click "OK."
Connect your instruments and microphones to your Tascam US-144. Connect analog instruments (such as guitars and stereo microphones) to the 1/4-inch "Line-In" connectors, the XLR microphones to the XLR slots (featuring three small holes) and speakers and turntables to the RCA (yellow and white) slots. The Tascam US-144 also can connect MIDI cables, but, as of June 2011, Audacity is not MIDI compatible, so you can ignore the MIDI connectors.
Adjust the settings on your Tascam US-144. On the top of the device, you will find a series of dials for each connected device and setting. Switch the "Phantom" dial to the "On" position if you have a condenser microphone attached; otherwise leave it off. Use the "Mic/Guitar" switch to designate the type of device connected to your right "Input" (if applicable), since you can optimize it for either device. If using only a single "Line-In" port, move the "Mono" switch to the "On" position and use the left "Line-In" port for your connection. Use the additional dials for volume controls.
Click the "Record" button at the top of your Audacity window and begin playing your connected instrument or transmitting audio through a connected microphone. The "Record" button looks like a pink circle. When you finish recording, click "Stop" (the orange square). You can record as many sessions as you need.