Yes, you can host other websites in your x10Hosting account. If you're on an AdEnhanced plan, you'll need to put your usual ads up on every page that is hosted on your account, otherwise if you're on AdFree you won't need any.
Credits are for the Forum. At the moment you can't do much with them, but soon we will have a sort of shop where you can buy a domain name or Paypal payouts. You could also use them to pay other users for services etc.
Personal Advertisement Code is like for forums credit? and is Corporate Hosting Package change before it only ads now i have this like highlight words and when mouse on it there a little ads is that normal because it wasn't use to be that..