It's a death saving throw. The bar on the left, the blue bar, means you saved. The right bar, the red, means you failed. A downed character needs to fail or save 3 times. If you saved 3 times, you regain consciousness and regain 1 hit point. If you fail 3 times, you die. The roll to beat is a 10.
Some things can affect the out come: if an enemy attacks the downed character, it will add a fail. If a friend uses a healing spell or the help action, then that is an auto succeed. I am unsure if they have implemented this as well, but in 5e rolling a natural 1 or a natural 20 also highly effects the outcome.
