The prototype of Lets verb is fixed collocation. Complete writing: a common spoken form of let us. Grammar: the basic meaning of let is to allow the other party to do what they want, and the extension can mean "rent" and "let go".

Let's is the abbreviation of let us, and it is also a common spoken form of let us. When there is only a monosyllabic verb after let in the passive voice, you can use the infinitive without to.