Clothing system question

This is very first time try to use clothing system in UE4. I follow every step of tutorial and it seems after everyone paint weight the cloth follow direction of gravity afterwards. For myself I try several time to get it work, but when I release painting cloth activate; it doesn’t appear to follow direction at all. Can anyone tell me what is happening or whats should I do. I really want to understand this function since it is really useful. Thank a lot.