# What are the potential functions of the cliques in Markov random field?

I have been trying to understand the representation of the joint probability density of Markov random fields in the form of factors of the potential functions. I am finding it difficult to grasp the idea of potential functions and how we are supposed to choose a potential function. Any suggestions on how I should get started. I have gone through the wiki page and some other resources, but still I couldn't grasp the essence of it.

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 1/Z * exp(a + b*x1 + b*x2 + c*x1*x2)