1). Because - is a conjunction, used at the beginning of a clause, before a subject and verb.
We were late because it rained.
I'm happy because I met you.
2). Because of - is a two - word preposition, used before a noun or a pronoun.
We were late because of the rain.
I'm happy because of you.
Note : Because and its clause can go after or before the main clause.
I finished early because I worked fast.
Because I worked fast, I finished early.
View sentence number 48 at the link below