As you are a beginner, spells, especially ones meant to bring bad energy to another are definitely not the place to start. There are no beginner spells, even a simple spell needs the caster to have a good grasp of the basics.
No spell is going to work for you if you don't have the basic skills to cast one. You need to be able to raise, direct and send energy with focussed intent. You need to be able to ground the left over energy.
You need to understand why the spell is structured the way it is as well. For example, why is a love spell best cast on a Friday? What crystals and herbs are best to use with such spell? What incense? What phase of the moon is best? What time of day is best? etc etc Basically in my opinion until you are able to write your own spells you shouldn't be casting anything.
Instead you need to study and practice, there are many pinned posts in the forums on the basics so go through and have a good read of them. A good book to start with is 'Spells and How They Work' by Janet and Stewart Farrar.
Good contribution. Though I must ask: wouldn't days, phases of the moon, inscence etc all fall in with ritual components ? As such, surely they would only hold the value the caster has personally placed on them ?
Reaverarchon. One of the questions the original poster had was with regards to the ritual components of a particular spell (black candles) and were they important. My point is that if the caster has no understanding of why they are there in the first place then they will have no real meaning and therefore no impact on the spell work at all.
If you are a beginner, you need to learn the basics first, do not, in any case, work with a demon. Never summon what you cannot Banish.
What does the day matter? What does the color of the candle matter? It matters a lot. For your spells to work, first the is the Will to work the spell. Then your have to have the correct Moon phase, the correct day, the correct time etc.
Casting a curse takes more energy than casting a spell, but basically they are the same thing.