In order to start training courses, go to main menu (top-left corner) and select "Courses". 

Once in Courses space, click on a training path.

Training path should display the entire courses list. 

A training path consists of one or several modules. A module is composed by different courses. Unlike courses, modules are highlighted in bold.

Once you have selected a cours, preliminary informations will appear (type of course, estimated time and a short description). Then, click on "Start" or on the course poster.