The documentation for FieldTrip is split into several parts:
The tutorials will help you to get started by providing examples that you can copy-and-paste into Matlab. The introduction tutorial is the best place to start if you do not have any idea about the ideas behind the FieldTrip toolbox. Also, reading through the Walkthrough will give you a good overview of the ideas behind the toolbox and analysis methods. Sometimes we prepare dedicated course material for workshops, which we also share.
The frequently asked questions section provides a lot of practical information. Furthermore, the example MATLAB scripts contains pieces of documentation that are often not so elaborate as the tutorials, but that go in more detail into specific aspects of the data, code or analysis.
If you are very eager to get started with your specific data, please proceed to the user documentation section on importing your own data. It provides details that are specific to particular data acquisition systems and explains how we deal with system specific peculiarities.