okay...
zoom in on your timeline (bottom left in the timeline window or +/-)
select the razor tool (c)
cut around the frame you want
back to selection tool (v)
and either
copy/paste the amount of frames you want to duplicate
or
rightclick the frame, select frame hold..., check 'hold on', click ok, and expand the frame(clip) (drag from the right side for how long you want), it should hold the frame