It depends what type of plant you are trying to propagate. But generally, you take short healthy shoots about 4 inches long, trim off the bottom leaves and trim to just below a leaf joint. Dust with hormone rooting powder (not always necessary) and put 5 or 6 cuttings in a small pot of free draining compost. This must be fresh and not re-used compost. Water gently and pop the pot in a clear plastic bag and tie the top with wire twisty tie. Check regularly that it is still moist and after a few weeks ( or months, depending on type of plant) the cutting MAY have rooted! A good way to check is to gently tug at the cutting, if it comes out of the compost it's not ready, if you feel reisistance it has started to root. Leave them until they show good growth, then pot on separately. Take more cuttings than you need, to allow for failures. Also, try at different times of year, too. Good luck!