OK, solved this one - the function I wanted was "snapping". Next
question: suppose I have a block (i.e a section of a waveform) in the
multitrack window. Is there a way of adjusting the beginning or end of
the block? For example, if the block begins a second later than I
decide I want, can I shift the start point to include the missing
second from the original waveform?

Hope this makes sense.