/summon

The Command
/summon is exactly what it sounds like: a tool for summoning the desired entity at the desired location. If one wants to summon a sheep where they're standing, they can type the following into chat:
/summon sheep ~ ~ ~
The three tildes (~) at the end are substitutes for X, Y, and Z coordinates respectively. They mean "right here," and they can be used as such often in commands. Just make sure they're separated by spaces.
If you want to summon a mob somewhere else, just type in the command, the desired mob, and then the coordinates of the desired location. We will use a zombie for the following example:
/summon zombie 2107 4 -8
This will cause a zombie to appear at the coordinates 2107, 4, -8.

Not Working?
If this command is not working, check to make sure that you've typed in everything properly, and make sure you're opped so that you have permission to use the command. Commands do not work in Survival worlds unless Cheats are on, in which case you can no longer earn achievements in that world.
In the case of this particular command, it is worthy to note that when summoning hostile mobs, check to make sure your difficulty is not set to "Peaceful." If it is, that means hostile mobs cannot exist in that world.
Also, make sure you have the name of the entity you want to summon correct. Even though the Ender Dragon is referred to as "the Ender Dragon," (her name is actually Jean, according to Notch, but that's not relevant) she is referred to for coding and command purposes as "dragon."
Please also note that this page is intended for Bedrock Minecraft, and these commands may not work in Java Edition, PS4 Edition, or Xbox 360 Edition.
Lastly, if the above directions are unclear, out of date, or otherwise, please take the time to leave a comment down below explaining the issue. We do take the time to review our comments.