Binding is the process of attaching a spirit to a vessel or to a human's spirit. By binding it gives the spirit a home, a chance to be able to share their life with someone and exchange respect and love. Just like anyone all entities want to feel needed, loved, cared for and that they matter.
There are hundreds of ways to bind a spirit to a vessel or human and most of them involve an invocation. There are only a handful that are publically shared as most conjurer's prefer to keep their binding methods a secret to themselves or amongst their Order, Coven, etc.
Spirits are not harmed during the binding process and are not required to give up anything in return for being bound. Spirits are bound to an object to give the spirit a home and sanctuary of their own. When a spirit is bound to a human's spirit they will usually select an area of the body they like the most and retreat to that part of the body when they feel they need a moment alone.
Binding can take place by using an invocation and binding bag. A binding bag is a satchel that is enchanted with a spell designed specifically for promoting a bind between any spirit that exists to the object in the bag.
You can bind through invocation alone which usually requires the conjurer to hold the vessel in their hands while reciting the invocation.
Binding can be through ritual using oils, candles, stones and/or statuary associated with the spirit.
A spirit can be banished from a vessel releasing them of all ties. When a spirit is banished they are no longer tied to the human or vessel any more and are free to be conjured by another conjurer or exist without bond. Banishing a spirit is not painful but it is a serious practice that can result in feeling of rejection for both the Keeper and spirit. Before a spirit is banished all other methods of making ammends should be explored.
The process by which a conjurer binds a spirit is, in part, what dictates the energy with which the spirit will come through to the Keeper and whether or not the spirit could be stolen by a malicious, superior conjurer. Though this is a remote chance it does happen between warring collectors which is why publishing or otherwise publically announcing the name of your spirits is not recommended unless you are 100% positive the conjurer who bound the spirit has done so with protection to keep this from happening.
Anyone is capable of learning binding and the first spirits they bind will of course be weak with energy but an entity can be rebound as their powers grow allowing the spirit's capabilities to surface.
Those interested in binding should use meditation techniques to come to a comfortable place before performing the binding action. Being in the right frame of mind is the proper and most effective way to ensure you bind correctly.