Great article on how the immune system works, describing the various immune responses, and also how vaccines prime the system. It's short and is by far the most clearly written article like this that I've seen. Well worth your time reading it (unless you're one of the doctors or scientists here, and in that case it might be worth reading it so you can pass it on to others you know).

https://www.latimes.com/science/story/2022-01...id=2571963