Ernest is described as being a "defensive mastermind with a strong devotion to protecting his allies." Based on the lone piece of concept art released so far, he looks to be a chubby, headband-wearing bird creature who wields a grenade launcher.
Beyond that, we don't know what his abilities are, though you can try to glean something from the concept art and this outline of his background: "As the Varelsi scourge darkened system after system, Ernest joined up with the Peacekeepers to put his demolition prowess in service of the universe. A brilliant technician, this demobird will take on any challenge by going right the hell through it!"
More information regarding his abilities are promised when we get closer to his launch. When that will be is unknown; Gearbox is only saying he'll be out "in the next couple months."
As with the first two DLC characters (and the two more still to come, post-Ernest), he'll be free, but you'll still need to unlock him in-game. Ernest will cost 47,500 credits, or you can use a hero key, which season pass owners receive with the release of each character. You can read more about how those work here.
As for the today's new character, Pendles is available to season pass owners now, with a release for all players coming on August 4.
If you don't already own Battleborn (or are looking to convince a friend to buy it to play with you), it's still available on PC for $15 as part of a Humble Bundle. The PS4 and Xbox One versions are also on sale for $30 at Amazon and Best Buy, while PlayStation Plus members can also get it for that price on the PlayStation Store.