You can use the source code to create one Project (a website) for yourself or for a client of yours. The project itself may be sold.
You can edit every piece of the given code to your liking.
If you create a project for a client, the License is then transferred to your client.
You may create on instance of a customized version with this theme, but not more than one.
You can't redistribute the theme as a theme (i.e. reselling with the source files included).