Robson, K., & Pevalin, D. (2016). Random intercept models: When intercepts vary. Multilevel modeling in plain language (pp. 21-65). SAGE Publications Ltd.
This chapter discusses the random intercept models. These are models in which the intercept is allowed to vary for each Level 2 group; this is the random part of the model. The chapter starts with a quick review of ordinary regression before easing into the random intercept models. It offers a step-by-step approach to exploring the data and specifying models with main effects and interaction effects.
Centre for Multilevel Modelling. (n.d.). Random intercept models. University of Bristol.
This is a very rich resource for multilevel modeling and it breaks down complex concepts of multilevel modeling into simpler forms which are easy to understand, and it also provides concrete examples which students can relate to.