Since this is not my area of expertise, I searched Google under the key words "How do Schwann Cells initiate Myelination" to get these possible sources:
In the future, you can find the information you desire more quickly, if you use appropriate key words to do your own search. Also see http://hanlib.sou.edu/searchtools/.
Don't just copy the material. Express the ideas in your own words. Although this will take more time and effort, you will learn more.