Though it is pronounced "슴니다" base ending is actually -(스)ㅂ니다. ㅂ is a bit irregular in that it changes to more of an ㅁ sound when followed by ㄴto make pronunciation flow more easily. -(스)ㅂ니다 is a verb ending used in very polite speech, higher than -요 or -시오.
The basic structure is verb stem + -ㅂ니다 for verb stems ending in a vowel, and verb stem + -습니다 for words ending in a consonant, and you simply add the ending to whatever verb ends a sentence to elevate the level of politeness.
Some good examples you might encounter when first starting to learn Korean are 죄송합니다 - I am sorry (very polite). 만나서 반갑습니다. - I'm glad to meet you / It's nice to meet you.
As an example, 제 이름은 숀입니다 is a more polite version of 제 이름은 숀이에요. - My name is Sean.
For questions, you use a similar ending: -ㅂ니까?
e.g. 어디에 가고 싶습니까? - Where would you like to go?
You can still add the -시- honorific to both ㅂ니다 and ㅂ니까 to make them even more polite as well.
e.g. 무슨 일을 하십니까? - What kind of work do you do?
영어를 잘 하십니다 - You speak English well.
Using 하다 as an example for reference, the common endings in order of increasing levels of casualness and familiarity (i.e. the most polite at the top, the most casual form used with close friends/family at the bottom) would be:
하십니다
합니다
하세요
해요
해