I have been lambing for 16 years, and am now a vet, so have considerable experience of sheep prolapses! The basic pre-lambing vaginal/cervical prolapse is relatively easy to deal with, and can be fixed and kept right by spoons, but if you get a prolapse after lambing, it is considerably more difficult to deal with, and with considerably less chance of survival. Best option for these really is to get the vet, as an epidural can really help.
Sugar is a trick for one that's been out a while, particularly useful for say a beef cow that's out at pasture, and may have prolapsed for 24 hours before it's noticed. It attracts the water out of the prolapse (because the pressure has blocked fluid getting back to the body and it has swollen) and makes it shrink, so makes it easier to replace. In most sheep prolapses this won't be necessary, it will be possible to put the prolapse back in without shrinking it.
Use the flat of your hand or your fist as required, try not to use your fingers too much as they are small and put more pressure on the fragile tissues, so you can put holes in. Once your entire prolapse has gone back in, you should be able to fit a whole fist and part of your wrist in.
At this point, you can apply the spoon. If you don't have a harness, then you need to tie it on with baler twine. My preferred way of doing it is to fashion a harness out of baler twine, the thicker the better. Create a loop that does not slip, which will go over the ewe's head, and the long end goes along her back. With another piece of twine, place the middle roughly in the middle of her back, in front of her hips. pass both ends under the back legs and up either side of her tail. Tie both ends to the middle of this piece of twine and each other. then tie the middle of this double loop to the original piece of twine down the middle of the ewe's back. Finally, you can put the spoon into the vulva, try to lie it fairly flat along the bottom, but it will sit where it sits in the end! Put a piece of twine through each of the holes, and knot them so they are tight, with one loose end each. Tie these loose ends to the piece of twine going in front of the ewe's hind legs, as tight as possible. This should keep the spoons in, and shouldn't interfere with her normal functions.
An alternative that I have never managed to get to work is tying these ends to the wool without the harness, though many people do this with great success.
I usually mark the ewe, because although when you first put the spoon in it is obvious, sometimes the twine blends into the wool well, and her tail hides the spoon, so a big coloured spray mark will help you keep a closer eye on her as she comes up to lambing. They can lamb through the spoon, but if you spot water bags, it is helpful to take it out and check how she is progressing.
Hope that helps
Suzanne