1. I have a wallet on blockchain.info, i think it is the wallet called "online wallet"?
2. I have installed "bitcoin-qt" software, i think it is the wallet called "offline wallet"?
3. Can i send BTC from my blockchain.info wallet to my "bitcoin-qt"?
4. Does 1 wallet can have multiple addresses? (on bitcoin wallet software i can create some addresses).
5. which one is the safest way to store BTC : blockchain.info / my bitcoin software?
Thank you.
1. Yes, it's an online wallet.
2. No, offline is cold storage such as paper wallets or if you keep your wallet.dat file on a usb etc
3. Yes, you can send BTC from your blockchain to your computer wallet.
4. Wallets can have multiple addresses. Just create a new one.
5. The safety depends on how safe you are. You can lose both your accounts to key loggers if they get your passwords. On blockchain.info you can set up 2 factor authentication which adds an extra layer of security. Make sure to encrypt your wallet and make several back ups.
Spend some time reading up on the different ways you can safely store your money before diving straight in. Better to be safe than sorry.
Hope that helps.