Davidson College - Affinity Chromatography Method
Well illustrated introduction to the basic, general method.
Chemistry LibreTexts - Affinity ChromatographyContains a concise and information discussion of the variety of tags used in affinity chromatography, such as polyhistidine. Having foreknowledge in this area is the kind of thing that helps you keep your footing on the exam.
Amrita Vishwa Vidyapeetham University - Purification of IgG Antibodies using Affinity ChromatographyIntroduction that is a bit more in-depth.