You use a frame that has an inside border - if you are choosing your own
framing, take a look at a ready made one to see how they work - the
framing must have that border to hold the canvas stretcher - you put it in
with long staples or nails to hold it against the framing. Or you can buy
lathe strips - stain or paint them before you attach ttach and simply
nail them to the stretcher through the canvas - you can also paint after
they are attached but it is harder.