Hello, thank you for your answers. Could you tell me :
1) If it had worked how could I find my bitcoins and use it to buy online? Because my Electrum account is on my PC. I do not know how the bitcoins would arrive on my PC?
Technically, there are no such objects as a Bitcoin. It is all based upon transactions. Transactions create outputs and consume outputs of other transactions. They then get recorded permanently in the blockchain. When you spend Bitcoin from a wallet like Electrum, what you are doing is you are creating a transaction which consumes outputs created by other transactions and then broadcasting that to everyone so that miners will then add it to the blockchain. There is no need for your wallet to be synced or to even be online in order to receive Bitcoin as there is no "Bitcoins" that arrives at your computer. When you next go online, your wallet will just ask nodes who keep the entire blockchain for your transactions that have been added to the blockchain.
Wallets handle tracking all of the transactions and creating the transactions. Just use the send tab in Electrum to send Bitcoin.
2) can you tell me commment (which reliable site) to buy the bitcoins with paysafecard?
No reputable site that I know of will accept paysafecard or any other form of prepaid card. You can try localbitcoins where you will be trading with other people, but that is also not guaranteed to be scam free. To avoid being scammed, always use localbitcoins' escrow feature.