Have problem with Punch Collision

I’m learning UE4 according to the official vedios recently. Now I want to add physics components for punching and when I create two spheres at my characters’ both hands and finish the construction script of my character, I found the spheres become so HUGE with the color white and I can’t even change its size any more. How can I change it to be transparent and a bit smaller? Thanks a lot. (First time to post a question ,I’m new learner and the tags really confuse me and I don’t know which one to choose,also my English may not be good enough:))