Well, to summarize a passage, you'd first have to read the passage. Afterwards, you'd most likely want to make sure that you understood it. Taking notes isn't required, but it's helpful if you aren't strong in understanding them. Next up, you'd probably try to find the main idea. Summarizing is something that you could do easily, even in your everyday life. You watch a cool movie this month? Summarize it.
Let's say I had just watched Endgame and I was SUPER eager to share it with somebody, but I can't give away the whole movie or else they wouldn't want to watch it and they'd most likely get mad at you. You'd have to summarize it. State the main idea and thesis and make sure that they can figure out what the plot is without you having to tell them the plot. You're welcome. (:
