The tutorials contain background on the different analysis methods, and include code that you can copy-and-paste in MATLAB to walk through the different analysis options. The frequently asked questions and example scripts are other forms of documentation.
Some of these tutorials are also used during the “Advanced EEG/MEG analysis” toolkit course that is presented at the Centre for Cognitive Neuroimaging of the Donders Institute for Brain, Cognition and Behaviour each year. Furthermore, we use these tutorials during the various workshops.
For information on what types of datasets we have here on FieldTrip, and which datasets are used in which tutorials see this faq What types of datasets (and their respective analyses) are used on FieldTrip.
When adding tutorials please consider the documentation guidelines.