Generally, when you choose a source on a TV, it’ll enable a given audio and video source. Eg, “AV1” might be SCART, “AV4” might be an yellow S-video phono and a pair of red / white stereo phonos.
Assuming you do actually mean VGA, presumably you’ll select “VGA1” or similar on the TV. There will be a corresponding audio jack to go with that, probably next to the VGA input. Randomly connecting the video to the VGA input and the audio to AV4 won’t (usually) work as they’re separate inputs. Cycling through sources would give you video but no sound, or sound but no video.
There should be embossed text next to everything telling you what they are.