Hi intherage,
"Because" and "because of" are both used to introduce reasons.
"Because" is a conjunction and is followed by a subject and verb.
conjunction = a word such as "and", "but", "nor", "while" or "although", that connects words, phrases and clauses in a sentence. In the sentence "I like coffee, but I don't like tea." "but" is a conjunction.
"Because of" is a preposition and is followed by a noun phrase or verb-ing.
preposition = a word which is used before a noun, pronoun or noun phrase to connect it to another word. In the sentences "She sat on the chair." and "He walked along the street" "on" and "along" are preposition.
Examples:
"I couldn't go out because I had a cold."
Did you see the subject and verb after because? She said "I had a cold."
"I couldn't go out because of my cold."
Did you catch the noun phrase? - "my cold"
You could also use a gerund - that's a verb plus "ing" after because of .
"I couldn't go out because of having a cold."
A verb with "ing" often functions as a noun so you use it after "because of."
Regards.
V.