How do I use a crimson/demon altar in Terraria?

I came across a crimson altar in Terraria, and have spent 26 minutes looking this up with no results: how, in the world, do I use it? I seriously do not understand. And this has been a common theme with this game from the get-go, like the Extractinator with its bizarre place the silt into the machine like you're placing a block interface. It's occurring to me that Terraria is very unintuitive and kind of all over the place with its user interface.

The wiki says the suspicious-looking eye can be crafted with it, but despite all my frantic clicking, I can't get the thing to work. I've tried standing on it, hitting it, clicking every button on the mouse, and throwing the whole stack of lenses on top of the altar with no results.

I hope this doesn't have to do with expert/normal mode. Cause if so, well, why did it even spawn, first of all, but if so, then I wasted an hour beating a dead horse.

To say this is frustrating would be an understatement.

The crimson/demon altar is a crafting station. You can use it to create early-game boss summoning items and the Night's Edge.

You use it like any other crafting station - simply stand next to it, open your inventory and click whatever item you need to craft.

It is simply a crafting station like any other in the game (work bench, anvil, etc.). To use it you just stand near it and open your crafting menu and you'll see the new options available pertaining to the demon altar.

If you don't see any new crafting options available in your crafting menu make sure you're standing close enough to it.

And don't feel dumb, the same thing happened to me the first time I found one!