Learn Hardcore Korean: siheomi kkeutnamyeon chinguwa yeohaengeul gyehoekhago sipeoyo. - After the test, I want to plan a trip with my friend.

시험 means “test” or “exam.”
끝나다 is the verb “to end” (stem 끝나-).
-으면 is the conditional/temporal ending meaning “when” or “if.”
Putting it together, 시험이 끝나면 literally means “when the test ends” or “after the exam is over.”

How does the ending -(으)면 work in Korean?

Attaches to verb or adjective stems: if the stem ends in a vowel, use -면; after a consonant, use -으면.
Conveys “if” or “when” depending on context.
Introduces a condition or time clause.
Example: 비가 오면 (“if/when it rains”), 끝나면 (“when it ends”).

Why is it 친구와 여행을 계획하고 싶어요 instead of using -를 with 친구?

와/과 (or the colloquial 랑/이랑) is the comitative particle meaning “with.”
친구와 = “with a friend.”
If you used 친구를, that would mark “friend” as a direct object, changing the meaning.
So 친구와 correctly indicates who you’re going together with.

Can 친구와 be replaced by 친구랑? Is there a difference?

친구와 is slightly more formal or written.
친구랑 is more casual/spoken.
Both mean “with a friend” and are interchangeable in everyday conversation.

What does 계획하고 싶어요 mean, and how is it formed?

계획하다 = “to plan” (literal root 계획하-).
-고 싶어요 attaches to the verb stem to express desire: “want to ….”
Breakdown:
1. 계획하- (stem)
2. -고 싶어요 = “want to …”
  Together: “I want to plan …”

Why is 끝나면 in the present tense if it refers to the future?

Korean often uses the present tense for future events when a time expression is present (like 끝나면, “when it ends”).
The actual time frame (“after the test”) makes it clear you’re talking about the future.

What politeness level is -고 싶어요, and how might it change in other styles?

Could you use 시험이 끝나자마자 instead of 시험이 끝나면?

끝나자마자 means “as soon as …” with an immediate action following.
끝나면 is more general “when/if …,” without the sense of “immediately.”
Choose 끝나자마자 if you want to emphasize “right after the test is over.”