The Art of Summoning is also referred to as evocation however these two differ in connotation and historically so we will treat them as individual methods.
The Summoning Arts can be traced back with the roots of Religion and Spirituality. Every Religion from polytheism to monotheism Christianity to heathenry incorporates basic summoning principles every day. Symbols representing their Deity of choice in prayer, jewelry and even architecture are all attempts to call and gain attention from their deity. Ancient Romans used to paint or carry symbols of their patron deity into battle in the belief that it would gain the deities favor and help them be victorious.
Now a brief overview of the two types of Calling:
1. Evocation is the most passive form of calling an entity as an Evocation typically is a ritual inviting an entity to appear rather than forcing it. Normally an Evocation ritual starts with a cleansing of a space and then a creation of a destination area for example symbols drawn on the ground or in the air etc. finally having set the stage as it were the caster recites the incantation inviting the spirit to join them and afterwards recites an incantation thanking and releasing the entity.
a. Note the nice thing about Evocation is if you?re looking for help but are unsure of what to call Evocation allows for a general calling instead of a specific by inviting and stating your dilemma then waiting seeing what comes.
2. Summoning is a more forceful calling as it removes the choice, or attempts to, from the entity. A summoning ritual begins the same with a cleansing and a setting of a destination however often as well as a destination the use of binding spells or symbols will be applied in order to keep the entity there once it?s manifested until forcefully dismissed. Unlike evocation often summoning spells will be short and to the point the same with dismissals. Some experienced summoners no longer rely on set binding spells and instead can force and keep an entity there simply through force of will. Be very careful though often beginners attempted and fail due to insufficient strength.
The basics are required before attempting either also one should make sure to do thorough research on the entity you are wanting before attempting. Summoning something you know little or nothing about can be very dangerous and should be avoided.
Invocation is most often associated with prayer and Deity work. Many ritualistic prayers and hymns contain Invocations in pretty much all religions. On the flip side in ancient religions Ivocation is associated with summoning an entity again often a deity of some form under threat. For example in Aradia, or the Gospel of the Witches by Charles Godfrey Leland the Conjuration of Diana is not simply commanding but threatening that unless a wish is granted Diana shall experiance "that she shall Know neither rest nor peace, and ever be In cruel suffering". So almost exclusivly with Deities and possibly threatening.
Evocation to me is used for all manner of spirits, from deities to demons. Also Evocation is often associated with works such as the Keys of Solomon tomes. Also Evocation while a command relies on the power of names or of the Will of the caster to hold a entity instead of under threaten. In Enochian magic spirits are often Evoked into scrying tools and held there until the summoner releases it.
So basically the Evocation of a spirit doesn't give the entity a choice assuming your successful however it doesn't presume to threaten the spirit either. Levels of control.
Here is the Invocation of Diana from Aradia, or the Gospel of the Witches by Charles Godfrey Leland.
"I do not bake the bread, nor with it salt,
Nor do I cook the honey with the wine,
I bake the body and the blood and soul,
The soul of (great) Diana, that she shall
Know neither rest nor peace, and ever be
In cruel suffering till she will grant
What I request, what I do most desire,
I beg it of her from my very heart!
And if the grace be granted, O Diana!
In honour of thee I will hold this feast,
Feast and drain the goblet deep,
We will dance and wildly leap,
And if thou grant'st the grace which I require,
Then when the dance is wildest, all the lamps
Shall be extinguished and we'll freely love!"
Here is a link to an post with an Evocation ritual. I will say this is not how I work this may call to some of you more as it seems to be a bit more tradtional.