According to Althusser Repressive state apparatus are those institutions that works trough coercion, force or the threat such the police, military and courts
in the other hand, Ideological state apparatus are the opposite institutions that works tr ough persuasion, teachings and behavioral developments to make individuals accept the social norms. such school, family, religious organizations and few cultural systems
the difference is mainly the approach it have to the individual, mode of operation, the visibility and function
RSA are direct, visible and forced
ISA are indirect, subtle and persuasive
An example of an Ideology is Catholicism it is subtle but firm, it provides the Christian ethics and moral through the sacred scriptures, it is a philosophy based on loving your neighbor.
in some cases this ideology is conveyed from home, from a very little age, and it shapes how you see the world, how you see yourself and how you treat other people