Starting again after 3 years break

Hello tankersAfter 3 years of total break I'm considering giving WoT another tryHowever, I have no idea what exactly changed during those 3 years – when I stopped playing the current feature were marks on tanks, and the firsts set of missions for T-55a and Object 260I guess since then a lot more content was added / changedAll I know is that there were some big changes with crew perks (but no details), that there are some pink / purple modules (no idea how to get then and what's going on in detail) and apart from that I don't know anything :/I wouldn't care that much but I used to be a decent player (54% WR with 12k battles, few X tiers), so I'd like not to throw it all away ;(Are there any good, up to date tutorials? I'm sometimes still watching some WoT Youtube channels, but first, it's not often, and secondly, there are rather games then explanations
So any help here for a not-so-new newbie? 😀

EDIT: And what is frontline and obligations? Is it only for clans?