A clause must contain-

A clause must contain a subject and a verb.

Clause:
- A clause is a part of a sentence.
- An expression including a subject and predicate functioning as a part of a complex sentence

Types of clauses:
- There are two main types: independent (main clauses), and dependent (subordinate clauses).

Independent clauses
- A clause in a complex sentence that can stand alone as a complete sentence.
In other words,
- An independent clause is a clause that can stand on its own as a distinct sentence.
Examples:
- I love eating cookies.
- My dog barks a lot.

Dependent clause.
- It needs an independent clause to finish or complete the sentence.
Ex. When I got home, I ate dinner.
- Dependent clauses are sometimes known as subordinate clauses. Example: When I grow up

Source: Oxford Practice grammar and A passage to the English Language by S.M. Zakir Hussain.