summon spells basically do as the name say it summons an entity from the astral world be it a demon, a spirit or an spiritual creature. to summon gods and godesses you need a ritual so they can present to you but it's more of a luck thing in the case of gods and godesses. Some of the things you can summon are djinns, elementals, demons (but demons are a little hard to control you have to prove stronger than them be it spiritually or physically ) and for the last creatures like the phoenix any more questions just send a mail. i'm no master but i'm rather experienced with summoning
Yes you can summon someone into your life. It violates free will though. This is my opinion. It really depends on what you are doing. If you are calling back a person who you like, than it's violating free will. If it's calling new people into your life by magick, then it's not violating free will. This is my opinion though. Hope this helps.