Horsing is a borrowed term that essentially means channeling. And yes, channeling deities and wights is a plausible thing. Within Northern Tradition Shamanism, channeling can sometimes be seen as a way to communicate with specific deities, to give them an offering, and to form a kind of bond with them.
How to safely go about doing it can be a kind of indepth question, at least for the Northern pantheon. There are several different deities, and each deity tends to be horsed in a different way. Not to mention that you cannot *make* a channeling happen.
I would suggest you read these three articles by Fairywolf that talk about Horsing, how it's done, why it's done, etc.
If you'd like to talk more about it, feel free to mail me. Horsing is a part of my practice and devotional for several deities within the pantheon I work in.