Video guides
Some things are easier to watch than to read. These are short and to the point, and the collection grows as the Tower does. Everything here also lives on the YouTube channel.
Skills: finding, slotting and casting
How a skill goes from a gem in your inventory to a button that fires: the gear menu, the sockets, binding and cast mode. This is the one the tutorial points you at if you get stuck. The written version is on the skills page.
The Necromancer fight
The Floor 3 dungeon boss from door to drop, as it actually plays. What to expect before you go in is on the boss guide.
Looking for something that is not covered yet? Ask in the Discord, or check the written wiki, which covers every system in detail.