Starting at 11th level, your rage can keep you fighting despite grievous wounds. If you drop to 0 hit points while you're raging and don't die outright, you can make a DC 10 Constitution saving throw. If you succeed, you drop to 1 hit point instead. Each time you use this feature after the first, the DC increases by 5. When you finish a short or long rest, the DC resets to 10.
RollQuest ships the D&D 2014 SRD as a content pack, on a 5e character sheet that does the maths - roll from the sheet and let the numbers work themselves out. Free to start.