How does this all work?

You need to explore the world for this mod to do anything since its actions are only performed on fresh chunks of the world as they are first generated. If in doubt, start a fresh world. Settings apply instantly but again, only on fresh sections of the world and never retroactively. This is why it is generally safe to use this mod on existing worlds.

Even then the sections of the world that have rails placed are by default Y=0 for EastWest mode and X=0 for NorthSouth mode.

Do I need to craft anything?

No. This mod uses Dark Hamster energy for all construction. No research or supply issues. Nothing special to build. Existing rails etc are not replaced if you remove them.

Can I change settings while in the game?

Yes. You're responsible for the transition between the changes though. You might need to match up power and red/green wiring as well. Changes are not immediately apparent because they don't update previous sections. This is deliberate and protects your existing base.

Landfill settings

"Place landfill if needed" will place landfill under rails, signals and power when the rails require it but otherwise not create other landfill. [not implemented in 0.18.0 of mod - this is still todo]
"Place landfill" will create a vast area of landfill joining all the rails. This will be overridden when the "if needed" setting is checked.

Floor type

The floor is placed joining all rails. Landfill is not actually required underneath. Floor auto-placed across water can be walked on. If floor tiles are removed, then landfill will be required as usual to restore the floor.

I selected a modded floor or rail but the ordinary version appeared instead

If Central Rails has an issue then it reverts to vanilla versions as a fallback.
This will happen with Dectorio if you select a variant of Dectorio's concrete in Central Rails but disable it in Dectorio itself. Either re-enable it in Dectorio or choose another floor type.
The same can happen if you remove a mod that provides a set of rails or other tile.

Bridge rail [0.18.0 onwards]

Select your chosen bridge rail in the settings. This will be used when the mod detects water. Otherwise the normal rail will be used.

Signalling is a mess

Yes it is when you set up parallel central lines too close. Part of this will be fixed in future release.

Why aren't ores and oil removed if they cover the rails?

Because they are resources you are meant to gather. Or build a suitable set of rails around. Moving resources is on the todo list.

This mod caused a crash

Add an item in the discussion on mods.factorio.com. I'll see it.

I can mine the power poles, signals, concrete and use it for other things!

Yes. If someone actually cares enough I might make this an admin-only feature.

I've got ideas for new features!

Put them in the forum for this mod.