This is a quick but tutorial on how to summon anything you want in minecraft.

First type - /give yournamehere 137 1 this will
give you a command block.

then press f3 and find out the x y and z coordinates of where you want to spawn
the item or mob.

then set the command block and copy and paste the following one you want
*NOTE - Only copy from the / on not the whole thing.*

And everything is case SENSITIVE
------------------------------

ZombieHorse - /summon EntityHorse x y z {Type:3}
SkeletonHorse - /summon Entityhorse x y z {Type:4}
Giant - /summon Giant x y z
EnderDragon - /summon EnderDragon x y z
Wither - /summon WitherBoss x y z
EnderCrystal - /summon EnderCrystal x y z
CHARGED CREEPER - /summon Creeper x y z {power:1}

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If you want it riding something and this

{Riding:{id:"name"}}

Fill in name with the creature vehichle or xp you want it riding

here are the ids
-----------------------------

What to put in for name is on top
what we call it bellow

ID -Bat
-Bat

ID -Blaze
-Blaze

ID-CaveSpider
-Cave Spider

ID-Chicken
-Chicken

ID-Cow
-Cow

ID -Creeper
-Creeper

ID-EnderDragon
-Ender Dragon

ID-Enderman
-Enderman

ID-Ghast
-Ghast

ID-Giant
-Giant

ID-EntityHorse
-Horse

ID-LavaSlime
-Magma Cube

ID-MushroomCow
-Mooshroom

ID-Ozelot
-Ocelot

ID-Pig
-Pig

ID-PigZombie
-Zombie Pigman

ID-Sheep
-Sheep

ID-Silverfish
-Silverfish

ID-Skeleton
- Skeleton/Witherskeleton

ID-Slime
-Slime

ID-SnowMan
-Snow Golem

ID-Spider
-Spider

ID-Squid
-Squid

ID-Villager
-Villager

ID-VillagerGolem
-Iron Golem

ID-Witch
-Witch

ID-WitherBoss
-Wither

Id-Wolf
-Wolf

ID-Zombie
-Zombie/Zombie Villager
-----------------------------

You can also ride xp orbs and minecarts and

If you want anything specific comment and ill add it
ex.) Zombie riding enderdragon

also if theres anything you dont understand tell me i will try to help.
thx.
DONT FORGET TO DIAMOND!!!