MMR in Norms

How exactly is MMR for normal games decided? I am sorry for complaining but I am just curious on how it works. I have had 3-4 games against high diamond players, which is not fun when you continuously get stomped on btw. I mean I understand plat 1-3 since I am sitting at plat 5 but d5-d2 players... I am not sure about that one. If this has been answered before or it is explained somewhere could I be told where? Thanks in advance