To synchronise content locally on a device, a client is required. The client for the respective device can be downloaded here.
After installation, select Log in to your Nextcloud and enter https://faircloud.eu/nextcloud as the server address. Then sign in with your fairlogin account. The folders to be synchronised can be selected accordingly.
This explanatory video shows how to install the Nextcloud Desktop Client version 3.11.0 software on the Ubuntu version 22.04.3 operating system: