After installing Daedalus wallet for the first time it will take some time to sync the entire blockchain with your Daedalus wallet. For some users, this may take many hours.
Daedalus is a full node wallet and requires a copy of the Cardano blockchain on your machine to operate. The blockchain is now over 6Gb in size on disk as of August 2019 so if your internet speed is quite slow it could take many hours. For most users with broadband connections and a relatively new machine, a full sync should take about one hour.
If the sync process is not working the most likely reason is either a 1) a network issue or 2) blockchain data on your local machine is corrupt.
1. See our article on 'Cannot Connect to Network' message
2. See our article on Delete and re-sync blockchain data