To start a training as a trainer, first go to the training overview and press "+". A window will appear in which you can choose between "Start training" and "Plan training". Now press "Start training". Then an overview appears where you can select the client with whom you want to start the training. You can either search for the client's ExID, select him under last trained or invite him if he is not yet registered in the app. As soon as you have selected the respective client, the training will be started directly.
To join a workout as a client, either press the push notification you receive once the trainer has started the workout, or go to the workout overview and press the light-up box located above the calendar.