What is 니다 and why does it seem like everything ends in it?
I guess you're alluding to -ㅂ니다 (or -습니다). These are verb endings that indicate high formality. Check out the lesson notes on the web for more detailed explanations.
It only seems like everything ends in it because the early lessons focus mainly on the 습니다 ending of formality. The formality endings in Korean are as follows from most respectful to least (excluding honorifics): 습니다, 요, ㄴ다, and just the stem (what's left after removing 다 from the infinitive) if you're being really informal.