BECAUSE / BECAUSE OF

The conjunction "because" is used at the beginning of a clause, before a subject and verb.

The two-word preposition "because-of" is used before a noun or a pronoun.

Please see comparison below:
1.
A - We were wet because it rained. (You don't say "..because of it rained.")
B - We were wet because of the rain. (You don't say "..because the rain.")

2.
A - I'm sad because I missed you.
B – I'm sad because of you.

Because and it's clause by position can go after or before the main clause.

Please see examples below:
1. I finished late because I worked slowly.
2. Because I worked slowly, I finished late.

Because-clauses can sometime stand alone, especially as answers or after hesitations.

Please see examples below:
1. Why are you sad? – Because Kai and I had a fight.
2. I don't think I'll go to school… Because I am feeling sick.

A quite common structure in informal speech – "just because… (it) doesn't mean…"

Please see examples below:
1) Just because you're senior than me (it) doesn't mean you can demand anything you want.
2) Just because I'm your sister (it) doesn't mean you can keep taking my things.