Rooting stem cuttings can be tricky. Do several more than you need with the understanding that many will fail to root. The smaller the branch, the better your chance of success. Some tree stems will root in plain water. But often with less hardy plants, the thinly rooted stems can't survive the transplant to soil. So it's usually better to use a low nutrient growing medium. I use a combination of sand and peat moss about two inches deep. Remove the bottom leaves from the stem. It's not absolutely necessary, but dipping the bottom of the stem in a rooting hormone powder greatly improves your chances of success.(You can purchase this at garden centers.) Then carefully place the stem in a hole in your rooting medium and push the medium in to fill the small hole around the stem. Add a little water to moisten the medium. Then cover the plant snuggly with a plastic bag. Use a rubberband to seal the bottom to hold in the moisture. Make sure the plant doesn't touch the plastic.