If you hover your mouse over the 'Online' icon it tells you the height/ date of the most recent block it knows about.
If you take your mouse away, wait a while and then do it again, has the block height increased ?

If so then it it syncing (perhaps slowly for some reason - peers vary).

If it isn't syncing at all then check your port 8333 is open and isn't being redirected anywhere (say to a Bitcoin Core on your network, something like that)