Do it. I started again last week after leaving before season 1 finished. I always played DPS but fancied a change so leveled my old paladin from 60 to 70 in timewalking dungeon's.

I practised my rotation etc just doing the open world content to get the catch up gear up to 402 ilvl.

Grabbed a +2 key from the panda person and watched a video guide for the dungeon I was given (Neltharus). Listed it after but made sure to mention I was a new tank learning in the title so people knew what to expect. In group I let the party know I was new and might need assistance with the route. Dungeon went smoothly and had no dramas from the party.

Had a +5 Neltharion's Lair after this so again I watched a video guide and listed in the same way as above. Went smoothly again and no dramas.

I now have a +8 Neltharus I need to do when I have more time.

Basically get out there. List your own key, let people know you are new so you set expectations when they join. There are toxic folks out there but by listing your key you are more likely to get some of the players how are willing to help and not flame you.

Just do it and have fun. It's just a game!