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 might give you some extra overview.
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.
Although FieldTrip contains all functionality to perform a full data analysis, other software tools might be more convenient for you or might provide additional functionality. It is perfectly fine (and actually recommended) to use FieldTrip in conjunction with those other tools. Here are some considerations in using FieldTrip in conjunction with other software packages.