Heroic though they might be, adventurers can’t spend every hour of the day in the thick of exploration, social interaction, and combat. They need rest: time to sleep and eat, tend their wounds, refresh their minds and spirits for spellcasting, and brace themselves for further adventure. Adventurers can take short rests in the midst of an adventuring day and a long rest to end the day.
A short rest is a period of downtime, at least 1 hour long, during which a character does nothing more strenuous than eating, drinking, reading, and tending to wounds.
A character can spend one or more Hit Dice at the end of a short rest, up to the character’s maximum number of Hit Dice, which is equal to the character’s level. For each Hit Die spent in this way, the player rolls the die and adds the character’s Constitution modifier to it. The character regains hit points equal to the total. The player can decide to spend an additional Hit Die after each roll. A character regains some spent Hit Dice upon finishing a long rest.
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.