I have the app but I don't find it very useful. I only use it when I'm travelling and don't want to connect to the FF mobile site. It only records
AF and
BD, plus has a notes section. I find their mobile site much more useful as you can record all of the normal details that way.
But if you want to link to your FF account, you click on sync then enter your FF username and password. If you want to upload data, I'm guessing you click on Save Data. I've only ever downloaded data (by clicking on Import Data). It also has a link to the mobile website.