I have a solid door. I want to divide it along the current edges:
The answers of @DredWolf and @RobinBetts are both good solutions if you're creating from a plane, these answers are how you should do it. Nevertheless, here's something additional to that solution. If you already have an extruded object like the one in your screenshot and you maybe want small grooves between those parts to separate them, you can do the following:
- Select the edges where you want to create grooves.
- Use Ctrl+B to bevel those edges so that each edge becomes a doubled edge.
- Keep the selection of the new face loops, hit Alt+E > Extrude Faces Along Normals.
- Scale them inwards to your liking (or outwards for ridges).
If you want to make real gaps so that there is space between them, you can use this method. It uses LoopTools (Preferences > Add-ons > Mesh: LoopTools).
- Select edges as before.
- Bevel as before.
- Right-click on the object for the context menu. Choose LoopTools > Bridge. In this case it only deletes the faces, of course you can do it without LoopTools. Just hit X > Delete > Faces. The advantage of LoopTools is, it keeps the edges selected.
- With the edges still selected after Bridge (or select them after deleting faces), now hit F to fill the open sides.
- You've separated the door with gaps between the parts.