private key is for login to wallet ?
private key is the most important aspect of Bitcoin it lets you spend your Bitcoins
But for most, private key is not important because all Bitcoin clients use it and dont bother you with such technical aspects of Bitcoin
Let's be clear.
Sure, you don't need to memorize or write down your private keys -- the wallet handles that.
But, if you don't control the private keys, you don't own the bitcoins.