1. First, go to Live > Preferences and select the Audio tab on the left
2. For Driver Type, select CoreAudio on Mac (ASIO if on Windows.)
For Audio Input Device and Audio Output Device, select the MT 48

The Input Config and Output Config buttons allow you to customize your input and output options, including renaming them.
Only highlight the ones you wish to use in both mono and stereo configurations for inputs, and stereo only for outputs.

Once you have the appropriate inputs and outputs enabled and renamed as desired, you can begin recording.
On a track, navigate to the I/O settings. The input will be the input your source is coming in from on the MT 48 (Mic 1, Mic 2, Line 3-4, etc.)
The Output will by default go to your Master Bus, which then outputs to your main outputs on your MT 48. You can change this as you see fit.

Prior to recording, you will need to check your input level coming in to the interface. You do this through the MT 48's Preamp module for the appropriate input selected. If you are recording more than one source at the same time, you will need to do this for each input. See "Setting Up a Track to Record" in the Tutorials guide.