Learn Hardcore Korean: jeoneun gongwoneseo dallyeoyo.

저 vs. 나: 나 is informal “I,” used only with close friends or younger people. In everyday polite conversation, you use 저.
는 vs. 가: 는 makes 저 the topic (“As for me…”), while 가 would mark it as the straightforward subject without that nuance.

Why is 공원에서 used instead of 공원에?

The particle 에서 indicates the location where an action occurs (“at the park”).

공원에서 달려요 = “(I) run at the park.”
공원에 달려요 would imply movement toward the park (“run to the park”), because 에 often marks destination or static existence.

What is the verb stem of 달려요, and how did it get conjugated?

The dictionary form is 달리다 (“to run”).

Remove -다 → stem 달리-
Add the polite present ending -어요.
Because the stem ends in the vowel ㅣ, 리 + 어요 contracts to 려요.
Result: 달려요.

Can 저는 be omitted, and if so, what changes?

Yes. Korean often drops subjects and topics when they’re clear from context.

(저는) 공원에서 달려요 still means “I run in the park.”
Omitting 저는 makes it more natural and less repetitive once the speaker is understood.

What is the basic word order in 저는 공원에서 달려요? Can it ever change?

The typical structure is Subject/Topic – Location – Verb (S-L-V).

저는 (topic)
공원에서 (location)
달려요 (verb)
You can swap topics for emphasis, but the verb almost always stays at the end.

How would you express the past tense, “I ran in the park”?

Change the present -어요 to the past -었어요 after the stem:

What politeness level is 달려요, and how would you say it more formally?

달려요 is polite informal speech (해요체).

Could you use a different subject marker instead of 는 in this sentence?

Yes. If you switch to 제가 (subject marker 가) you focus purely on the subject without the topical nuance:

제가 공원에서 달려요 still means “I run in the park,” but sounds like you’re introducing yourself as the runner rather than contrasting or generalizing.