If i were to purchase Bitcoins off of a seller from this site, how do i transfer
the bitcoins to a third party site securely?Hi,
Well, the seller would send the bitcoins that you purchased to the bitcoin address that you provide to the seller.
Generally, you want to get a new bitcoin address for each transaction.
With the Bitcoin.org client, you click Receive Coins,then New Address and then Copy to Clipboard.
Once you've received the bitcoins you need to wait at least one confirmation before spending them to the third-party site.
Other options are to use a wallet such as My Wallet from Blockchain.info
That functions in a similar way .. Receive Money -> Generate New Address.
Blockchain's wallet also lets you spend after just one confirmation.
You can also provide a bitcoin address from a hosted EWallet, such as what most Bitcoin exchanges offer, or an EWallet hosting provider like Paytunia.
The delay for confirmation with these will vary ... for example, Mt. Gox will not credit your account for Bitcoins sent until after six block confirmations.
Now, when you used the phrase "securely" that could mean a few things. If you are sending a lot of bitcoins, perhaps none of the above are secure enough. For instance, are you sure your computer isn't compromised with spyware? To protect against even that you'ld want to ensure that you are using two-factor authentication (e.g., Mt. Gox yubikey), for instance.
If you used the phrase "securely" because you wish to use Bitcoin anonymously, then that means something else as well. For that, there would be a different set of suggestions.