gongwoneseo sanchaekhamyeon gibuni johajyeoyo.

-에서 marks the place where an action happens. Since 산책하다 means to take a walk, the walking happens in the park, so 공원에서 is correct.

• 공원에서 산책해요 = I take a walk in the park
• 공원에 가요 = I go to the park

So:

• -에 often marks a destination or location of existence
• -에서 marks the location where an action is performed

산책하면 comes from:

• 산책 = a walk, walking
• 하다 = to do
• 산책하다 = to take a walk
• 산책하면 = if/when one takes a walk

So this is a very common Korean pattern:

• noun + 하다 = to do that noun

Examples:

• 공부하다 = to study
• 운동하다 = to exercise
• 산책하다 = to take a walk

-하면 is a conditional form. It often means:

• if
• when
• whenever

In this sentence, it sounds most natural as a general condition:

• If I take a walk in the park, I feel better
• When I take a walk in the park, I feel better
• Taking a walk in the park makes me feel better

So it is not necessarily talking about one single future event. It often expresses a repeated or general result.

기분이 uses the subject particle 이/가 because 기분 is the thing that becomes good.

Literally, the structure is closer to:

• Mood/feeling becomes good

So:

• 기분 = mood, feeling
• 기분이 좋아져요 = my mood gets better / I feel better

Even though English says I feel better, Korean often makes the feeling/mood the subject.

This is a very common learner question.

• 좋아요 = is good
• 좋아져요 = becomes good / gets better

So:

• 기분이 좋아요 = I feel good / my mood is good
• 기분이 좋아져요 = I start to feel good / my mood improves

In this sentence, 좋아져요 emphasizes a change of state. After taking a walk in the park, your mood improves.

The dictionary form is 좋아지다.

It breaks down like this:

• 좋다 = to be good
• 좋아지다 = to become good

Then:

• 좋아지다 → 좋아져요 in polite present style

This happens because Korean often uses -아/어지다 to mean become.

Examples:

• 커지다 = become big
• 작아지다 = become small
• 좋아지다 = become good / get better

Korean often leaves out the subject when it is obvious from context.

So 공원에서 산책하면 기분이 좋아져요 can naturally mean:

• I feel better when I take a walk in the park
• You feel better when you take a walk in the park
• One feels better when taking a walk in the park

The exact subject depends on the situation. In everyday Korean, omitting the subject is very normal.

By itself, it usually sounds like a general statement or habitual truth.

So it suggests something like:

• Whenever I take a walk in the park, I feel better
• Taking a walk in the park makes me feel better

If you wanted to talk about one specific event, you would usually add more context, such as time words or surrounding sentences.

It can be used with all of them, but the form changes slightly depending on what comes before it.

Examples:

• 가면 = if/when one goes
• 먹으면 = if/when one eats
• 좋으면 = if/when it is good
• 학생이면 = if someone is a student

In your sentence, 하다 is the verb inside 산책하다, so 하면 comes from that.

Yes, Korean word order is somewhat flexible, especially with adverbial phrases. For example:

• 공원에서 산책하면 기분이 좋아져요.
• 산책하면 공원에서 기분이 좋아져요.

But the first one is much more natural for the intended meaning. The original sentence clearly groups 공원에서 산책하면 as if/when [you] take a walk in the park.

So while Korean allows some movement, the original order is the most natural and easiest to understand.

좋아져요 is in the polite informal style, often called -요 style.

It is:

• polite
• natural in conversation
• very common in daily speech

Other possible styles:

• 좋아집니다 = more formal
• 좋아져 = casual, plain speech to close friends or someone younger

So the sentence as written is polite and natural for everyday use.