Q:What is a spell?
A: A spell refers to an attempt to harness the energy of the earth to bring about a (hopefully) positive change.
Q: Why do I feel tired after casting a spell?
A: When spell casting your using your bodies vital energy. This energy is what you get when you do things such as, work out or exercise, be among the elements; such as walking through nature, standing outside when the moon is out because you can soak up energy from the moon just like your crystals can and you'll see why you'll find that they like it. If you feel tired after you've casted a spell it could be that you used too much of your energy or that you didn't raise enough energy, or maybe you didn't call upon the elements to aid your spell.
Q: How do I raise my energy?
A:You can raise your energy by thinking of love, and I mean friendship love because love is the most powerful energy there is, including self love. If you want to raise your energy think about positive things, eventually you'll be so sensitive to energy that when you start being negative, such as getting angry you'll be able to feel your energy going down, and by the law of attraction you'll get what ever you focus on. So if you focus on the negative, guess what? That's what you'll get. But if you focus on the positive then that's what you'll get too, and your vibrational frequency will be higher, which is the rate of how fast your energy is moving, positive energies such as love vibrate faster and higher than energies of hatred.
Q:What can weaken my spells?
A: Well, you can. If you have no faith in your spells, like you think your not strong enough to have them do what your intending, then your weakening your own spell. So disbelieve can weaken your spell. If your casting a spell on someone that is meant to do something good, such as healing, there disbelief may weaken your spell. I've heard that black magic isn't affected by the disbelief of others as much. Though I would not recommend practicing such, as black magic intendeds to do harm, which would go against the Wiccan rede: An it harm none, do what ye will.