My boss asked me to design new website and willing to sell items online. I have strong knowledge of PHP, Javascript, HTML, CSS. Is there a tutorial for client and server app? For example, online retailers show different items everyday. Is this done manually?
Do a google for "online storefronts" and you'll find more.
You can serve the storefront from an iframe if you have an existing web site that customers are visiting and you don't want them to see that the URL for the storefront is different.
The client/server/security/database/fund transfers/commerce thing is pretty in depth and not something I'd recommend getting into.