Hi guys! I will be doing a tutorial today how to learn scoreboards easily! We don't want to waste times so, lets get right into it!

          First step, there is ways to show kills and deaths, and you can name them to make maps, and server minigames!          Here are the things, there are many more, but here are the useful ones. Deaths ID = deathCount. Kills on Players ID = playerKillCount. Kills on Mobs/Entities ID = totalKillCount. Hitpoints/Health ID = health. You need to use these for commands.
                                                     SUCH AS THESE COMMANDS FOR SCOREBOARDS.

/scoreboard objectives add (insert objective name here) totalKillCount, and /scoreboard objectives setDisplay sidebar (objective name). Now, the first command, /scoreboard objectives add will add an objective, after that you put the name and the id lastly, such as, totalKillCount for kills on all entites I used in the example. It will not appear unless you do this after:
/scoreboard objectives setDisplay. After that you put sidebar for it to be in the right side, list, if you want it on the list when you press tab on the keyboard it will popup with a list of kills on entites on players, and the last is belowname, so when you look below your playername you will see the kills you have done. Here's an example: /scoreboard objectives setDisplay sidebar (objective name). That's how scoreboards work. But, if you're sad that when you put in the command there isn't a scoreboard, kill and entity and then it will pop up on your sidebar with your name and a number with the amount of kills you have near it, including the name you called it on top. And if you don't want the totalKillCount, replace that with health, playerKillCount, or deathCount for those to be the objective score shown, if you want it to display the objective score somewhere else than the sidebar use belowname, or list. Hope it helps! Enjoy this if you don't know how to make a map or minigames for a server. Bye!!!