is it because the synchronization is not finished ?
Yes, so stay calm
What is that ?
You installed the Bitcoin-QT client, it is a full node client, it means that it not only act as a wallet but it also download the FULL blockchain of bitcoin, wich means every transactions done and relay it to other nodes. The bitcoin network is a p2p one, so the full nodes relay all the transactions between them.
It takes a lot of time
Yes, it is downloading more than 10GB of data and verifying them all.
Note that you do not need to have a full node, it is meant for people who want to run it constantly, having a full node when you use it only for 5minutes every some days is pointless. Get Multibit for example, much much quicker, for the same security
Oh and make sure you backup your wallet, have no virus on the pc and learnt about how to securely store your coins!