The User's Guide covers the basics fairly well. It has no index, so it can be difficult to find the exact reference you need. You can set only one layer as the working layer, and everything that you draw goes on that layer as you create it. Colors, linetypes, and pens are all set explicitly, not by layer, and therefore a layer can have entities that use many different colors, linetypes, and pen widths. Layer modes within any drawing include visible, editable, and read-only, in addition to the working layer property.
Drawings control the loading, visibility, and editability of each layer used in that drawing.
Layer names consist of a sequential number and a text name field, and you can attach an additional description that displays in the layer dialog boxes. Specific layer name systems, such as the AIA system, are not included with the program, although you can create custom systems. A drawing file is simply a small text file that lists the status of each layer property in that particular drawing. Multiple users can work on different drawings in a project by loading only the layers needed to provide the required visibility of a drawing and then controlling the read-only and editable properties of those layers so that other users can open the same layer files for viewing or editing. Sheet files are distinct from drawing files and are used to compose views for plotting or to navigate a project to load drawing files for editing.