Reading thousand of books and cursing someone are two different things ,
Just like reading about doing magic and actually doing it are two completely different things.
and as mentioned by a few fellow members,if your a beginner you should not try to curse an individual,
it has consequences if done wrong,even novice people or priests make mistake when cursing so there's a high chance it might happen to you.
Why do you want someone to have a nightmare? If your mad at them or they have done something wrong to you I suggest you sit and watch what happens yo this person from a distance because something bad will happen to this person without you doing anything. That's Karma
You guys aren't helping him by spelling out beliefs to him/her, when you could provide for what is asked. Advice is nice, buts nicer when you respond correctly. And be more fluent in your questions, please. You'll find that most here don't tolerate those uneducated in grammar.
Spoon-feeding is distasteful. I recommend you read through all the FAQs displayed; skip some here and there. There will be questions similar to yours, and the answers will provide you a better basis. After your questions are answered, move to articles so you understand the nature of magick. I recommend you read Herbs aswell, for they can be potent in a spell. Don't be afraid to change a spell. Members have made these spells that are posted. Don't be afraid to even make your own. Keep it in a Spellbook. Whether you want a Book of Shadows, a book that collects all spells that will be handy to you, or a simple notebook that will give you tips along with specific spells and purposes that you dedicate yourself to, you must learn with it. And keep it intact, for there is always answers to be found.
Lastly, once you're grasp is stronger, take a gander at the Spells section, and look for curses corresponding with that category you wish for. Feel free to type in "nightmare spell" or "nightmare curse" in the search box, at the very top right of this website.