I know how to do it but I am kind of far from you. I will try to explain. Basically you want to bend the metal so that it kind of matches the shape of the sill and the trim around the window. We usually take a 3/4" strip of metal and bend a shape in it with a hand brake. The shape matches the trim I want to cover. We call this a template. We use the template to make sure the capping will fit all the way around the window. We then use the template to make the capping on the brake.
After the capping is bent it is just a matter of cutting and installing it on the window trim. Just remember to start at the sill and work upwards. All the pieces should overlap so water cannot get in. Caulk after the capping is installed.