In this section we will cover some of the basics that you will actually need to know to write analysis code in ATLAS, e.g. messaging, handling CP tools in general and xAOD basics. In the next section we will then cover the different object types in the xAOD and what tools the CP groups provide to interact with them.
It is generally advisable to work through this entire section and work through it in order. Most of these concepts are fairly basic and worth knowing, but we will do our best to let you know if things are optional or advanced, so that you can skip through those if you are in a hurry. Indeed anything marked advanced is probably good to skip through the first time around.