Connect the USB adapter to your iPad. Apple sells a camera connection kit that includes one; other manufacturers provide a variety of solutions as well, such as three-in-one and five-in-one adapter dongles.
Connect the output of your audio-to-USB device to the USB port on the adapter. Your device may be a USB turntable that includes a preamp to provide level adjustment, as well as decoding equalization. This device should connect directly with a USB cable. To use an analog turntable and home stereo amplifier, connect an adapter from the "Tape Out" jacks to the line input on the audio-to-USB interface. This adapter will most likely have RCA plugs or a stereo mini-plug, though your equipment may vary.
Prepare iPro Recorder -- a standard iPad application -- to receive stereo audio by going to "Settings" on your iPad. Select "iPro Recorder" and under "Channels" set "Record in Stereo" to "On." Open the iPro Recorder app and select "New Memo," then tap the third icon at the bottom of the screen to choose your recording quality level.
Tap "Record" and start playing your album. Adjust volume so the signal does not exceed the purple meter section. Tap the "Stop" button when recording is complete. You may also use other audio editor and recorder applications to accept your vinyl input.