To synchronise content to your a device, a Nextcloud client is required, which can be downloaded here for your Laptop or PC. For your Android or iOS mobile device check the app store.
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. For smartphones, individual files can be downloaded for offline use.
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: