Past has three different meanings.
1. Past can be a noun, meaning "what has already happened."
Example
2. Past can be an adjective, meaning "gone by" or "ended."
Examples
3. Past can be a preposition, meaning "beyond" or "by."
Example
Review: Past can be an noun, adjective, or preposition.
Past is never a verb.
Passed is always a verb.
Passed is formed by adding -ed to the present tense verb, pass.
It indicates the past tense of pass.
Example of passed as the verb in a sentence
Example of passed preceded by an auxiliary verb
Remember: Past is never a verb.
BUT
Passed is always a verb.
Now try Exercise #1 on past / passed.