Learn Hardcore Korean: gongwoneseo kkocheul bwayo.

공원 means “park.” 에서 is a location particle that marks where an action takes place. So 공원에서 literally means “at the park” or “in the park” — it tells you where you’re doing the seeing.

Why is 꽃 followed by 을? What does 을 indicate?

을 is the object-marking particle used after a noun ending in a consonant. It shows that 꽃 (“flower”) is the direct object of the verb 보다 (“to see”). Thus 꽃을 means “(to) see a flower.”

What’s the difference between 공원에 and 공원에서?

공원에 (with 에) usually indicates a static location or destination: “to the park” or “at the park” in a general sense.
공원에서 (with 에서) specifically marks the place where an action happens. Since 보다 is an action (“to see”), you use 에서: “see (something) at the park.”

Why is 보다 conjugated as 봐요 instead of 보아요?

The verb stem is 보. According to Korean vowel‐harmony rules, 보 + 아요 contracts to 봐요 (not 보아요). So in polite informal speech, 보다 becomes 봐요.

Why isn’t there a subject like I (저는) in the sentence?

Korean often omits the subject when it’s clear from context. If you want to include it for clarity or emphasis, you can say 저는 공원에서 꽃을 봐요, but dropping 저는 is perfectly natural in everyday conversation.

What level of politeness is 봐요? Could I make it more or less formal?

봐요 is polite informal speech (해요체), suitable for most daily interactions.
More formal: 공원에서 꽃을 봅니다 (합쇼체).
Less formal/familiar: 공원에서 꽃을 봐 (반말).

How would I say this sentence in the past tense?

Change the ending -아요/어요 to -았어요/었어요. For 보다, that gives you 공원에서 꽃을 봤어요, meaning “I saw flowers in the park.”