Everyone has a pet/companion that they can enable of they want. You have a large selection of textures to chose for your pet
To open the pet selector user interface, enter the command /petblock an it will open a chest-like user interface.
Hover your mouse over the item and it will tell you what the item does when you click on it.
The wardrobe icon in the top left will let you chose what your pet looks like.
The # icon in the bottom left will let you name your pet and change other settings
The middle button will spawn or remove your companion
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