i have gota website and when people buy my product i want to be able to send them a username and password in which if they log in can chat to me or if i m not available there message saved is that possible and whatever they write is saved... is that possible m using wordpress atm....
Yes it possible, you can sell a product using WooCommerce plugin and you can use this plugin to chat with your customers: ScreetChat http://codecanyon.net/item/wordpress-live-chat-plugin-for-sales-and-support/3952877
Live chat may meet your needs. It enables you to engage visitors in real time. When you are offline, they can leave messages to you and the messages can be sent to your email. There are many chat plugins for WordPress sites. Comm100 Live Chat is such a solution. http://www.comm100.com/livechat/wordpresschat.aspx
I've used the live chat plugin from Code Canyon. It cost about $15, but is well worth it. Other free plugins I looked into didn't always work properly. You can also use membership plugins, such as s2 member (http://www.s2member.com/) where you can deter non-users from going to certain pages. It will instead redirect them to sign up for your website. You can create the page which hosts the live chat, and block anyone that hasn't signed up from accessing the page (which would have live chat). s2 member has a free version that should work fine.