The kinds of events that you can expect are:

• SDL_ACTIVEEVENT (focus change)
• SDL_KEYDOWN, SDL_KEYUP
• SDL_MOUSEMOTION
• SDL_MOUSEBUTTONDOWN, SDL_MOUSEBUTTONUP
• SDL_QUIT
• SDL_SYSWMEVENT (system-specific event)

You can decide which kinds of events you want to filter out (ie, you will never be informed of them when you use SDL_PollEvent() or SDL_WaitEvent()) by using SDL_SetEventFilter().