"pass" is the infinitive and the present form, "passed" its past tense, and "past" its past participle form.
So you should understand that all three have different functions.
"passed" is used when the main verb "pass" is in the past tense: e.g. I passed a church on my way (went by it).
"past" makes an adverbial phrase indicating passing by something: I drove past a church. (main verb is "drove").
"past" is often used with time too: "It was already past nine" (= later than nine, i.e. nine o'clock has already past).
So remember "passed" as the past tense form with limited usage as a main verb, and "past" as a participle that can relate something that is now in the back with the main verb ("past" is also an adjective and a noun; "passed" is none of these).