To record audio using multiple inputs (multitrack recording), follow these steps:

1. Start by getting your multi I/O device or sound card set up for multitrack recording.
2. In VEGAS, go to "Insert" > "Audio Track" to add the number of audio tracks you want to record to at the same time.
3. Click the record button in the header of the first audio track. You should now see a menu with available recording inputs. Select the input you want to use for this track. 
4. Repeat this step for each track you want to record to.
5. Click the "Arm for Record" button in the header of each track. 
6. Click the record button in the Transport bar beneath the timeline.
7. VEGAS will now start multitrack recording. When you are finished recording, press the stop button in the Transport bar to end multitrack recording.