Sorry if it's a idiot question : D I wanted to be sure.
So,if it won't be a problem if someone sent me coin while my wallet is unsynchronized ?
Just to add more informations to what was mentioned before
Here is a very simplified explanation on how transactions works :
When you make a transaction, the transaction it self has 3 components and Input ( the sender address), amount of of coins and output (receiver address) . (notice how there is no mention of coins them selfs, because they don't exist, the thing that exist in the bitcoin network are actually the transactions data )
the transaction data or record, are registered in the blockchain and each transaction is tied to private keys that are related to the previous input and output, so when a transaction is made and confirmed by the network which is processing the blockchain in this case you've received the coins on your address
your wallet being in sync or not has nothing to do with the transaction it self, The synching of the wallet is related blockchain, to receive the missing transaction in the network that the wallet missed when it was offline, hence during the synching when it reaches the transaction it self you'll see the bitcoins appears and the usual bubble message "you've received xxx amount of XXXcoins"
Obviously there are more things that makes the bitcoin protocol what it is, Just google it and you'll find plenty of information once you are familiar with the basics