Why is 니다 added onto so many words?
It's one of the possible verb endings. Well, actually, I guess you are referring to 습니다.
Depending on the verb ending, you get information about politeness level, tense, or nuances on meaning. It is probably the thing that is going to keep you busy for a big part of your Korean grammar study.
I will not explain it all as it would simply not fit in this short comment box.
For now, just remember that this ending implies higher formality, while the -요 form, that is also often used in this course, is of less formality (it's still quiet polite and you wouldn't use it with close friends).