How much are the fees?
The standard fee per one transaction is 0.0002 BTC (approximately 7 USD cents), wallets such as
charge these fees automatically. In case of the Bitcoin-Qt wallet this fee must be set. If you will not set this fee then the transaction will stay uncomfirmed for a long time (days) in a bitcoin network and eventually it might not be confirmed at all.
Who receives these fees?
All bitcoin transactions are processed by the so called miners
and the fees are transferred directly to them. Transactions including fees are moved to a single block and chained to a bitcoin blokchain, which in addition to 25 BTC rewards the miners with the provided fees.
Why is the fee required?
There are situations, when a great number of transactions are gathered for processing at the same time, in such cases the transactions with no fee are processed lastly. It may cause belated processing of such transactions and there is no guarantee when such a transaction is going to be processed. It may even occur that such a transaction is not going to be processed at all.
Transactions with a fee included have different size and a miner recognizes whether a transaction has or has not a fee included.
Most wallets or public services such as exchanges or depositories automatically charge a fee for any type of transaction. Fees are paid by most commercial transactions, which supporst the whole Bitcoin ecosystem. It is also planned for the future that the fees replace rewards for mining. That is why the miners will continuously be motivated to mine and confirm more transactions.
The recommended fee is 0.0001 BTC. If you send a multi-transaction (that is a transaction with multiple recipients) it is better to increase the fee. For most transactions the fee of 0.0001 BTC is sufficient.