Firebase persists all data permanently (and we back it up, etc.), so your data is "saved" just by using Firebase.
If you want to access the data from your own servers, we recommend actually having your servers talk to Firebase directly. So the data flow becomes (Client) -> (Firebase) -> (Other Clients and your servers)
We provide a Node.js client and a REST API to make this easy.
So instead of (Client)->[Your Server]->(All Clients), Firebase replaces your server so you effectively get (Client)->(All Clients).
This means if you wanted to save something you would have to make the (Client)->[Your Server] request separately.