How do I style my hair like this girl did?

You really wouldn't need much. If you want it wavy like that, then take a shower just before bed, brush your hair out after and part it at the side like the girl in the video, then while keeping that part put your hair in five or six braids. It doesn't matter if you look crazy. Sleep on your hair like that. Then in the morning undo the braids, brush your hair out a little bit, but don't mess with the part. Then just clip back a little chunk of hair at the front. Hair spray it to keep the waves.