Passed is the past tense of the verb “pass”, whereas past can indicate that time has passed. Confused yet?
“To pass” something is to move beyond it or go forward: The police car passed us with its lights on and siren blaring. I got good grades and passed all of my exams. Because “pass” is a regular verb, it means you can add “-ed” to the end to show that the event has already happened.
Past, however, can be tricky, as it can be used as an adjective, noun, preposition, or adverb. As an adjective, it can describe a time that has gone by (Spring has now past and it will soon be summer) or, when applied to a group of people, it can mean “former” (Past workers of the company returned for the CEO’s retirement).
As a noun, it refers to a general time that is not the present: In the past, clothing was very different than it is today.
As a preposition, past can be used for time (It is half past twelve) or location (The store is located just past the school).
And finally, past as an adverb means “to go by”, with location specified: During the football game, the ball passed several defenders before rolling past the keeper and into the net. In this case, past is modifying the verb “rolling”, telling you where the ball rolled: past the keeper.