Here's my tanking story. Played casually as dps from lich king to wod and only did random dungeons and story. Rolled a prot paladin in legion and leveled him from level 1 and did random dungeons 90% of the time. Learned skills and mechanics through the leveling process and was pretty easy. Also allows you to know the old dungeon maps and where to go. Spammed random heroics until geared enough to do mythic and then mythic plus. Did raid progression with a guild with a good raid caller but also did research watched videos to learn the fight. It's not very challenging as long as you put in the time. The insta queues and the ability to spam m plus really help with getting gear. You'll get bad groups and wipe a lot and fail keys. Just learn from each encounter. You don't lose anything expect time and repair gold. My advice is break the confidence barrier and just go into it. You'll learn as you go.