How to make a mincraft horse?

You need to have cheats enabled and then type /summon EntityHorse. Here is a full guide to further explain how to do this
https://www.digminecraft.com/game_commands/summon_horse.php
This is only possible if you have privileges to do so. If this is a world you created and/or a single player game that you set to allow cheats when making it should be easy enough but if that isn't the case it makes things more tricky. If this is a world you made but you didn't set it to enable cheats the easiest way I know of is to open the menu and click the open to lan button. It will take you to a screen with a few options and 1 of those will be allowing cheats. You will need to set the options how you want but make sure to allow cheats. Once that is done and you clicked the accept/ok button you should be able to summon your horse using the command given above. If you didn't make this world they will need to give you permission or perhaps they will be willing to do it for you. If none of that is possible don't fret you can still find horses in game, tame them, and breed them. To breed a tamed horse you will need to put at least 2 adult horses in a pin together and feed them both a golden apple or golden carrot.