Learn Hardcore Korean: naneun maeil hangugeo gongbu gyehoegeul saenggakhaeyo. - I think about my Korean study plan every day.

나는 is made of 나 (“I” in casual speech) + the topic marker 는.
저는 is the polite equivalent (“I” in formal speech) + 는. You can swap 나는 → 저는 to sound more polite.
You can also omit 나는/저는 if the context already makes the subject clear. Korean often drops subjects when they’re understood.

What’s the role of the marker 은/는 on 나는? Could I use 이/가 instead?

은/는 is the topic marker. It frames “as for me…” and often introduces general or habitual statements.
이/가 is the subject marker; it simply identifies the doer without that extra “topic” nuance.
If you said 내가 매일 한국어 공부 계획을 생각해요, it would feel more like emphasizing “I (not someone else) think…” rather than stating your daily routine.

What does 매일 mean, and why is it placed before 한국어 공부 계획?

매일 means “every day.”
In Korean, time adverbs like 매일 typically come before the verb but can also appear before the object. Placing it early (often at the sentence start) highlights the routine aspect: “Every day, (I) …”

Why isn’t there a 의 between 한국어 and 공부, or between 공부 and 계획? Wouldn’t 한국어의 공부의 계획 be more literal?

Korean forms noun compounds by placing modifying nouns directly in front of head nouns, omitting 의.
So 한국어 공부 계획 is a 3-noun chain:
1. 한국어 modifies 공부 (“Korean” → “Korean study”)
2. 한국어 공부 together modifies 계획 (“Korean study plan”)
Adding 의 would sound overly stiff or redundant in everyday speech.

Why is 계획을 marked with 을? What does that particle do?

을 is the object marker. It signals that 계획 (“plan”) is the direct object of the verb 생각해요 (“think”).
If a noun ends in a vowel, you’d use 를 instead, but since 계획 ends in a consonant, 을 is correct.

What does 생각해요 exactly mean here? Isn’t it just “think”?

The verb 생각하다 literally means “to think.”
In the collocation 계획을 생각하다, it conveys “to think up” or “to come up with a plan” — focusing on the mental process of devising the plan.
It’s different from just “having a thought”; here you’re deliberately formulating or brainstorming your study plan.

Could I use 계획을 세워요 or 계획해요 instead of 계획을 생각해요? Are they interchangeable?

계획을 세우다 = “to establish/set up a plan” (more formal, concrete).
계획하다 = “to plan (something).”
계획을 생각하다 emphasizes the act of thinking/coming up with ideas, whereas 세우다 or 하다 stress finalizing or carrying out the plan.
Depending on nuance, all three can work, but 생각해요 highlights the brainstorming stage.

Why is the verb in the present tense 생각해요? Does that mean I’m thinking right now, or is it habitual?

In Korean, the simple present tense (–아요/–어요) can express both an action happening now and a habitual or repeated action.
Here, because of 매일 (“every day”), it clearly means a routine: “I think up my Korean study plan every day.”