[subject] + 不用 + [verb]
不用 + 了 / 谢
不用 before a verb says there is no need to do it. It is the negative of 要 and 得 in the sense "have to".
不要 forbids: don't do it. 不用 lifts the need: you don't have to, but you could.
别 forbids in the same way as 不要.
不用了 on its own turns down something offered. 不用谢 answers thanks.
Neither 得 nor 必须 takes 不 in front; "don't have to" is 不用.