Chillen with the billen means your chilling at home watching YouTube or drawing, in other words your doing absolutely nothing. If your talking to a friend about it means your just doing the same as normal. Another way to say it, is chillen with THE billen.
To hang hard, preferably with several to many bros, engaging in activities such as beer pong, delving into the seminal works of David Hume, drum circles, rap battles, disk golf, and imbibing ganja through various techniques, only to name a few.