The words are already there with fixed spellings so that all we need to do is just learn them. The few times we might create a new word is when we create a new name(for people, pets, places), but ㅅ or ㅌ 받침 is not used much for names. So there is no need to worry about how to use them in your own way. If you meant how to distinguish between them when you hear them, the answer is that either the conjugated form or the context will tell you. For example, even though 잇다(connect), 있다(is), 잊다(forget) pronounce the same, they will become different when they change form, like 이으면, 있으면 [이쓰면], and 잊으면 [이즈면]. Sometimes, they may be indistinguishable (잇지만, 있지만, 잊지만 all pronounce the same) but the context usually make it clear. Languages even have many identically spelled words with multiple meanings (homonyms) which cannot be distinguished when in isolation (e.g. 못 may be a nail, a pond, or an adverb "can't") but it becomes clear which one is meant when it is in a sentence because of the surrounding information (context).

The final consonant is exposed when it followed by a vowel like '을 or 으로' 뭍 sounds [묻], 뭍을 sounds [무틀], 뭍으로 sounds [무트로] 옷 sounds [옫], 옷을 sounds [오슬], 옷으로 sounds [오스로]