I’ve written some here regarding the algorithm itself (link actually has two versions of the explanation, 4 years apart from different people, as they’re both true they’re just saying the same thing in different ways).
Kaawumba has a good explanation of it here. This should be your primary source.
Don’t listen to most people. The discussions have gone so far off the rails that even people that are ok with how the system works still don’t really understand how it works.
The most common mistake is the false belief that SR is used in matchmaking at all, but they’ve said repeatedly and unequivocally that it is not used and never has been used.