It's fairly straight forward for the most part. You include the following code and apply to the element you want to style. Eventually you will not need to use the browser prefixes but for now you do. Modify the value to achieve your desired result.
-moz-border-radius: 4px;
-webkit-border-radius: 4px;
-khtml-border-radius: 4px;
border-radius: 4px;