Of course you can! That's actually one of many Systems of Magic (Or Castes...Whichever term you prefer), and is known as Summoning. Here's a perfect article for you:
Well no not really as I said this on several threads that were similar to this one but spirits are not really good or evil, well at least not all of them, they are basically as diverse in personalities as are humans.
And as far as summoning goes, well I cannot really help you there at least not much, I mean there are hundreds of methods that serve to summon and bind a spirit to you, method I used was rather slow and probably very, VERY stupid(I basically just made a bait out of my energy and waited while meditating).
There are a few ways Summoning a spirit can become dangerous:
1. Summoning the wrong spirit. The Spirit World is much like our own; it has good and bad. Be careful and always be aware of what you are Summoning. Always summon the right spirit for the right goal, and it will happily help you. Not because you are above it, but because there is common interest.
2. Believing that you are above the spirit. This is a very dangerous mentality, and it can cause the spirit to either refuse to serve you, to trick you, or even harm you directly. NEVER consider yourself above a spirit. You are its equal. Nothing more, nothing less.
3. Believing that you are beneath the spirit. Again, a very dangerous mentality. This belief can cause the spirit to take advantage of you and either trick you or even possess and/or attack you. Once again, you are the spirit's equal, working together towards a goal. No more, no less.
Also, there are MANY more types of beings that can be summoned other than Demons. Some Practitioners can even summon Astral beings in addition to Spiritual/Etheric beings.
I personally agree with Hylians post, spirit summoning can be very dangerous; especially if you think your either higher or lower than the entity so it is best to treat him/her/it as an equal.
My spiritual companion "accidently" fell into our realm and suprisingly in my room so I was rather scared and wary at first, but after a week it turned out we had alot more commom than I realised and he's been living with me ever since then.
As stated above, spirits range in personality and temperament. But never disrespect a spirit. Spirits are dangerous when angered or when they have an opportunity to trick you or harm you when they are of a vile temperament.
So when attempting to summon something, always keep an amulet of protection on you of some sort, and approach a spirit with a healthy dose of skepticism and respect. Never trust a spirit right away. They can and do have the capability to lie. And some have the ability to twist the truth but never lie.
