how do i create in game characters,als,enemies, and animals

i also want to know how to make enemies attack your character and other players

To put all of that things you say about characters, enemies, animals and more there is something called import and export.

Here you can see what you can import into unity:

Also, for enemies attack you may start to see this kind of videos to start: and to know more about this is most in youtube and you can search for more about scripting in: