Summarize:

If you're using synthetic hair extensions or a wig, read the product label to see if it can be heated. The label should tell you how much heat the synthetic hair can handle. If you're unsure if they can handle the heat or you want to curl your weave, test curl a tiny portion of your hair to see if it melts. If testing to see if the synthetic hair will melt, ensure that you choose a hair that is slightly hidden so that if it does melt, it won't be noticeable. Decide how large you'd like your curls to be and divide your hair into sections. If you'd like small curls, divide your hair into many sections. If you want big curls, divide the hair into a few sections. Use a clip to secure the hair to your head. Turn your curling iron on to the lowest setting which might just be a warming setting (or level "1"). If you'll be curling extensions or a wig, place or secure the hair to a mannequin head. You'll need to wet your hair so that each portion is completely wet, but not dripping with water. You can wet your hands and run your fingers through the hair or you can use a spray bottle to spritz the hair until it's completely wet. Wetting your synthetic hair can prevent it from melting and can help it hold the curl. Wrap the preheated curling iron around one wet portion of synthetic hair and curl it up. Hold the curling iron in place until the hair begins to feel warm. Gently slide the curling iron out of the curl. Continue curling the rest of your hair. If you want to get a tighter curl, pin the curl in place against your head until it cools completely. This will also help the curl hold its shape longer.
Determine if you can curl the hair. Divide your hair and heat your curling iron. Spray your hair with water. Curl each portion of your hair.