Internet ratings are for fun. No ones gets a title based on their internet performance.
You get national titles (like national master, or NM) by achieving a high rating. In the United States that rating is 2200. If I wanted it I would go to USCF (united states chess federation) rated events which take place in person.
FM, IM, and GM are international titles (FIDE master, International Master and Grandmaster). They're awarded by the international body of chess, FIDE and are earned in FIDE rated tournaments which are over the board tournaments (OTB) meaning face to face, in real life games :)
You get the FM title by having a rating of 2300 FIDE or higher.
The IM and GM titles are a bit different. You have to achieve IM and GM norms (preform at IM or GM level against IM and GM players). After I think it's 3 norms, you get the title.
When these players register on chess.com, they can give the staff proof of their title, and then we see it by their username. Many of them have played few or no games, so their chess.com ratings are 1200 or 1700 as you said. But as I said in the beginning, internet ratings are for fun, and don't affect titles one way or another.
First things first, i am not trying to get a title by asking you how. Ok now, i have seen people with titles with a rating like 1700,dont you have to be a really high rating to get one? How do you get a rating?