The suffixes “-tion” and “-sion” are both used to create nouns from verbs (and, less commonly, adjectives and other nouns) to describe a state, condition, action, process, practice, or the result thereof. They are actually just permutations of the same suffix, “-ion,” but there are specific conditions that will dictate which one we use, so it’s worthwhile to consider them individually.
(There is also a third version, “-cion,” but this only occurs in two specific instances: coercion, from the verb coerce, and suspicion, from the verb suspect.)