Learn Hardcore Korean: undongeul hago naseo mureul masyeoyo.

을 is the object particle marking 운동 as the direct object of 하다 (“to exercise”). In Korean, particles like 을/를 show that the preceding noun is what the verb acts upon.

What part of speech is 운동, and why is 하다 attached?

운동 is a noun meaning “exercise.” To turn it into a verb phrase (“to exercise”), you add 하다. So 운동하다 literally means “do exercise.”

What does -고 나서 mean, and how is it different from just -고?

-고 나서 means “after doing [action],” emphasizing that the first action is fully completed before the next one begins. -고 alone simply connects two actions (“and”) without stressing the sequence or completion.

Can I say 운동하고 물을 마셔요 instead of 운동을 하고 나서 물을 마셔요?

You can, but 운동하고 물을 마셔요 reads more like “I exercise and drink water” (actions listed). By adding -고 나서, you make it clear you first finish exercising and then drink water.

Why is 물 marked with 을 here?

물 (“water”) is the direct object of 마시다 (“to drink”), so it takes the object particle 을 (or 를 after a vowel).

Why is the verb 마시다 conjugated as 마셔요?

마셔요 is the polite present-tense form. Start with 마시다, drop -다 → 마시, then add -어요, which phonetically contracts to -여요, giving 마셔요.

Who is the subject of this sentence? I don’t see one.

Korean often omits the subject when it’s understood from context. Here, it’s implicitly “I” (저), or whatever person you’re talking about.

Can I use 한 후에 instead of -고 나서?

Yes. 운동을 한 후에 물을 마셔요 is equally correct. 한 후에 is a bit more formal or written, while -고 나서 is more colloquial.

What if I reverse the order: 물을 마시고 운동을 해요?

That’s grammatically fine, but it changes the meaning to “I drink water and then exercise,” which is the opposite sequence.