What is a Magickal chain
Magickal chain is a protection ritual. Papus called it the absolute defense. The practice itself is split into two categories: the ritual and the use of the chain.
Point of the ritual is the creation or re-assurance of the chain, usage involves calling the master of the chain to activate it.
How to create the chain
First of all you should already have some experience with the Magickal prayer, these two are closely related. Secondly you should choose a master of the chain. This can be any long diseased occult master that somehow influenced your art (e.g. Crowley, Bardon, Papus, Spare, Paracelsus, Pythagoras...)
During the ritual you call and pray to the master of the chain. Then you call for guardians of cardinal directions, elementals, spirits, demons, angels... in other words you start at the bottom of whatever hierarchy and you work your way up till you reach whatever force you are used to pray to in Magickal prayer. Entities in the chain can be called specifically or generally, for example you can call specific entities you have already worked with or just elementals generally.
After all required entities are called you then request them to become your chain and appear to protect you any time the master of the chain calls them, you then ask the master to come at your call to activate the chain.
Then you can end the ritual as usually.
Using the chain
So, the chain is already created and you get into a really bad situation and you need to activate the chain. To do so you don't need to call all the entities again, just call the master of the chain with the request to activate it and that's it.
Time by time the chain should be re-assured, for that use the same ritual you used for the creation of the ritual, it's actually a good idea to keep the ritual description and used incantations in your journal.