what the hell is what

this igcse system is so confusing, i thought cie igcse students take o levels, but ive seen many people treating o level like a separate thing, is it like a different exam board from cie, actually why do different exam boards exist anyway, and why do both uk and international students take pearson edexcel, does thta mean they both take the same exam unlike with cambridge and oxford, better yet whats the point of separating uk and international students, also what the frick is ib, isnt that the same thing as pearson edexcel? i have so many questions