To buy Bitcoin with XBit Asia you need to have done two things:
Once you have done that, click "Trading" on the top right side of your screen
Now you can place your Order to "BUY" with the amount of funds that you have deposited into your account
Limit Buy (more advanced)
This feature is for more advanced users.
A limit buy allows you to select a price at which you'd like to buy your bitcoin, when the market (a willing seller) reaches your price.
Limit orders are done from the XBit Asia Exchange.
To learn more about the XBit Asia Exchange and more advanced limit orders, click here.