Sometimes similar words can be confusing. The words past and passed sound the same. However, past is a noun and passed is a verb.
Use the word past when talking about that time in the long ago.
In the past, we would write and mail letters to each other.
I have a lot of memories about the past.
The word passed is a verb. It shows action and is the past tense form of the verb pass.
I went fast and passed the slow car on the road.
I studied hard, and I passed the test.
Use the word past as a noun, talking about a time that happened before now. Use the word passed as a verb to show action that happened before now.
It’s your turn. Decide if you should use past or passed in this sentence. A red truck ____ us on the highway. Did you figure out that you need to use the verb passed? Good for you!