If you are using the latest version (Alpha 5), you are able to just drag the sound wave in the X-Sheet up or down, to adjust the starting point of the audio track. If it is locked, you need to turn off the lock first to be able to drag it.
It is only possible to import one audio file. You need to edit your audio first in an audio editor, to create your audio track from several single sound effects. The workflow is often this way – you animate to an audio track such as dialogue or music and that’s why it makes sense to do your animation AFTER the audio. It can be done this way with sound effects as well, but of course sound effects could be added afterwards in final editing. I hope this makes sense.