Download and install Audacity from audacity.forgesource.net for free.
Connect your turntable to your computer by plugging its cable into your computer's USB port.
Open the Audacity software. In the upper left-hand corner, click "Audacity" to open a drop-down menu. Select "Preferences." Under the "Audio/IO" section, you should see a section at the top of the window that says "Recording." Click the "Device:" drop-down menu and select your USB turntable from the list of options.
Select "Hardware Playthrough" under the "Playthrough" section and then click "OK" at the bottom of the screen.
Turn on your USB turntable. Place your LP onto the turntable and select a speed (45 or 33). Queue up your LP by placing the needle at the beginning of the record. Prepare Audacity for recording by clicking the "Pause" button, and then the "Record" button. When you're ready to record, press the "Pause" button again and then press the "Play" button on your USB turntable. Press "Stop" in Audacity when the record is finished recording.
Click "File" on the Audacity menu to open a drop-down menu. Select "Export" to open a new window. Type the name of the LP and its side into the "Save As" bar, and then under "Format" select the type of file you want to save it as. Click "Save" and you now have a digital version of your LP.