Grandmaster, International Master, and FIDE Master. They're official FIDE titles given to players who attain certain achievements. https://en.m.wikipedia.org/wiki/FIDE_titles
What does GM, IM and FM stand for?
So, how do you become a Grandmaster? Then, what do you need to do to become an International Master? Is there an International Grandmaster? IGM, and after you become an International Master or International Grandmaster, how do you become a FIDE Master?
lol, don't know if you are joking, but fide master comes first, then IM, then GM

Google sucks, this is what I get and it tells me nothing about chess:
If u don't know how to search...
IGM is not a title since all 3 major titles (FM, IM, GM) are all international titles, delivered by Fide. So I don't see why u added a "I" before GM.
A good way to search (for example) is typing "Fide titles" and then chose the wiki page (given in post 2!) which will give you all the informations u want, and even some u don't want!

CM = Candidate Master and requires a fide rating of 2200 or more
FM = Fide Master and requires a fide rating of 2300 or more
IM = International Master and requires a rating of 2400 or more and IM norms
GM = Grand Master and requires a rating of 2500 or more and GM norms
I don't know a lot about how norms work so here is something I copy pasted from the wikipedia page
To qualify for the title of Grandmaster of chess, a title awarded by FIDE, the World Chess Federation, a player must achieve two or more grandmaster norms in events covering a minimum of 27 games. Norms can only be gained in tournaments that fulfill FIDE's strict criteria; for instance, an International Arbiter must be officiating and the entry must include at least three GM titled players from different countries playing over a minimum of nine rounds with no less than 120 minutes thinking time per round. There are a number of other more minor stipulations.
The 'norm' seeker must achieve a tournament performance rating (TPR) of at least 2600 to qualify.
I assume it's similiar for IM norms too.
I would like to find out