Need help with gaming slang (Rocket League)

Good day! I want to know more about the world of Rocket League in order to understand what my young man is fond of, but, reading the posts, I do not understand the slang at all. Explain, please, the most popular abbreviations in this game, for example, what does "rank hh 1-2", "play mm in 1s" and so on mean. Thanks in advance!