Adding a new software layer
Root filesystem customization involves adding or modifying content to the base image. Metadata for this content goes into one or more software layers, depending on the amount of customization needed.
A typical embedded project will have just one software layer containing all non-hardware-specific customizations. But it is also possible to have extra layers for graphical frameworks or system-wide elements.
Before starting work on a new layer, it is good practice to check whether someone else provides a similar layer. Also, if you are trying to integrate an open source project, check whether a layer for it already exists. There is an index of available layers at http://layers.openembedded.org/.