Emission material not illuminating

Note: although the procedure described below does result in Eevee being used as the renderer, that wasn't intentional. So, not that it really matters, but this isn't a duplicate of the Eevee question, and the answer below telling me to change it to Cycles is correct.

I'm a complete newb. I'm interested in playing with shader nodes, but I'm failing at the first step: if I add an emission material it does not appear to iluminate anything.

Here's what I'm doing:

1. Create a new project

2. Delete the default light source, leave the default cube in place

3. Shift-A -> Mesh -> Plane

4. Move plane to somewhere above the cube

5. Go to shading workspace, which displays the shader node editor

6. Click on the plane

7. Delete the default "Principled BSDF" node

8. Add an 'Emission' node

9. Set the strength to anywhere from 50 to 500000

10. Connect 'Emission' output to 'Surface' input of the material output node

11. Render an image

I get this:

I have two questions:

1. Why is this happening? How can I get the emission surface to illuminate the cube?

2. Although the render looks like that, the preview looks like this:

On many YouTube videos I have seen people use a preview that looks the same as the finished render, but noisier because it uses less samples. How can I activate that? (I think the answer to the last one is probably "switch the preview renderer to Cycles," but I can't figure out how to do that.)

Here's where the plane is in relation to the cube. It's sort of hard to tell but it's about as far off the ground as the camera is, and from the camera's perspective it's above and to the right of the cube.