1. Objects and containers. A container is a three dimensional space within your design. It contains objects (boards) and / or other containers (doors, drawers, hardware). It may not contain another assembly.

The largest or highest level container is the project. A project may be a kitchen, one wall of the kitchen, an office, a desk or bookcase.
Every project must contain at least one assembly, and can contain multiple assemblies.
An assembly can contain a number of different types of objects.

Most of the time an assembly contains boards. Boards are the lowest level object. You can assign attributes to a board, for example a type of joinery or a hole, but the board cannot contain anything.

Assemblies can contain doors. A door is a container within the assembly. In turn the door contains boards and/or hardware.

Assemblies can contain drawer. A drawer is a container within the assembly that can contain boards and/or hardware.

Hardware is a container made up of parts. You can simulate any type of metal (or glass even) and use that material to build your hardware. Hardware is unique in that it is a container that can exist within the door, drawer, or directly at the assembly level.

The advantage of using doors, drawers and hardware as containers is that you can design them once and clone them, move them around, or modify them as one unit.

In order to design something at any level of the hierarchy, you must be in that level. In other words if you want to put boards into a drawer you must select the drawer that you're designing. Generally the act of selecting can put you into that drawer level, although sometimes you have to specify that you want to be in that level. To select the level click on it in the outline format control form.