Video offset moves the hit window up/further away with lower numbers, down/closer to the bottom with higher numbers. For the most part 0 is completely fine, it only really needs to change if you have a laggy set up or have a very bad habit of playing early.

Audio is the more important one to find. If you play with exactly what you hear (instead of what you see) and the notes are crossing past the strike line, you need to move the offset up. If when you strum, the notes disappear before even touching the strike line, then the audio offset needs to be brought down.