As always with basic care questions, stage of development, health, variety, soil, training goals, weather, etc. can affect the feeding protocol. Some basics:
If using dry food, feeding in spring, after flowering and in fall is a good place to start. Liquid fertilizers can be used to supplement.
Many types of fertilizers can work. Miracle-Gro, Miracid, and fish emulsion are common liquid fertilizers for azaleas. Solids include organics like cottonseed or rapeseed meal.
A Japanese azalea grower recommends against BioGold and other manure-based fertilizers for azaleas as they can burn the roots.