I recommend reading a book like Kraig's "Modern Magick"
You should never learn online. There is far more to it than just reciting a spell and it can be dangerous if done improperly, even if an "angel". Even then it still holds risk. I know someone who is currently getting their life flipped upside down because they evoked one, and he is experienced!
Lisa99, why are you posting this unrelated and almost certainly a role playing comment on an unrelated forum, this is not helpful for the person who posted the forum or to anyone else.
Otonashi, I suggest you do some serious research about protection, banishing and summoning rituals before you even think about doing any summoning, without the right knowledge it can go very very wrong.
Don't summon anything without a good (very good) reason. Spirits are dangerous, and they lie all the time. Banishing them is harder if they are angry. You need knowledge and strong mentality to do it moderately safely.
Noscete I`m sorry that I must correct you one one or two things, as spirits are not much different that humans in the way there minds work:
ONE is that spirits are not all necessarily dangerous. Yeah I mean sure there is always larger or smaller amount of risk present when summoning and working with them but it generally depends on knowledge and skill of summoner and/or on type of spirit he/she summoned.
TWO not all spirits lie or at very least not always, while true that they will always try to gain more out of the agreement if you let them you must also remember that humans do exactly the same thing all the time.
BUT also I must STRONGLY agree with you on the mater that summoning of the spirits can only be used as an absolutely last resort and with a VERY GOOD REASON and only when you have ALL measures and counter-measures prepared and every bit of knowledge and skill you can find and MASTERED(and yes I mean mastered as in you have reached a bloody peak of human capacity in them).