Learn Hardcore Korean: naega gandanhi seolmyeonghal tenikka jilmunhae.

-(으)ㄹ 테니까: Strong intention + giving a reason for a request/suggestion. Often used to divide roles: “I’ll do X, so you do Y.”
-(으)ㄹ게(요): Speaker’s promise/decision with consideration for the listener. It usually ends the sentence: 설명할게요. 질문하세요.
-(으)ㄹ 거니까: Neutral future reason (“because I will …”), less about resolve than -테니까.
-겠-: Willingness or supposition/formality. Polite: 설명하겠습니다. 질문하세요.

What is the politeness level of this sentence? How would I make it polite?

It’s in casual speech (banmal), via 질문해 and 내가. Polite versions:

제가 간단히 설명할 테니까 질문하세요. (plain polite command)
Softer request: 제가 간단히 설명할 테니까 질문해 주세요.

Does “질문해” sound bossy?

In casual contexts among peers, it’s fine. To avoid sounding blunt:

Add a softener: 질문 좀 해.
Use polite: 질문하세요, 질문해 주세요, or 질문 좀 해 주세요. Teachers/speakers to an audience usually use the polite forms.

Why 내가 and not 나는?

내가 (subject marker) highlights who will perform the action—“I (not someone else) will explain.”
나는 (topic marker) presents “as for me,” with less focus on performing the action. You could also drop the subject entirely: 간단히 설명할 테니까 질문해.

What’s the difference between 내가 and 제가?

Both mean “I” with the subject marker, but:

내가 is casual/informal.
제가 is the polite/humble counterpart (note the irregular contraction: 저 + 가 → 제가, not “저가”).

Where does 간단히 go, and can I say 간단하게 instead?

The adverb typically goes before the verb phrase: 간단히 설명하다 (“explain briefly”).
간단히 and 간단하게 are both fine; 간단히 can feel a bit tighter/more written, and 간단하게 is very common in speech. Meaning difference is minimal here.

Is “질문해” the only way to say “ask (a question)”?

No. Options and nuance:

질문해 (주세요/보세요/하세요): use the noun “question” + 하다; feels a bit formal/neutral.
물어봐(요)/물어보세요: very common “ask (me/us).”
Friendly invite: 궁금한 거 물어봐(요). / 궁금한 게 있으면 물어보세요.

Do I need to add “me,” like 나한테 질문해?

It’s usually understood from context. If you want to be explicit:

Casual: 나한테 질문해.
Polite: 저한테 질문하세요. Note: 한테 (spoken) ≈ 에게 (more formal/written). Honorific to the recipient: 께.

Can I switch the clause order?

Yes, but cause-first sounds smoother for requests.

Natural: 내가 간단히 설명할 테니까, 질문해.
Also fine as two sentences: 질문해. 내가 간단히 설명할 테니까. (a bit more abrupt at first)

What’s the difference between -(으)ㄹ 테니 and -(으)ㄹ 테니까?

Both can introduce a reason and lead into a request/suggestion. -테니 often feels a touch lighter/softer:

설명할 테니 질문해. (slightly softer)
설명할 테니까 질문해. (a bit firmer/clearer as a reason)

How is -(으)ㄹ 텐데 different from -(으)ㄹ 테니까?

-(으)ㄹ 텐데 expresses expectation/background (“will probably/be about to …, and/but…”). It doesn’t naturally license a command the way -테니까 does.

Awkward: 설명할 텐데 질문해.
Better: 설명할 테니까 질문해. or split: 이제 설명할 텐데, 질문 있으면 해.

Why is there a space in 설명할 테니까? I sometimes see “설명할테니까.”

Standard spacing treats 테 as a bound noun, so it’s written separately:

Correct: 할 테다 / 할 테니까
“할테니까” is a common typo in casual writing but not standard.

Could I say 설명해 줄 테니까 or 설명드릴 테니까?

Yes—these add a “for you”/benefactive nuance.

Casual: 내가 간단히 설명해 줄 테니까 질문해.
Polite/humble: 제가 간단히 설명해 드릴 테니까 질문해 주세요.
Note: Many speakers say 설명드리다, though some style guides prefer 설명해 드리다. Both are widely used.