(I apologize if my English is not good)
I wanted to make a rideable horse but I don’t know how, I have searched other Topics but they were all outdated as they were using Bodygyro, I’m trying to find ways on the tutorial website that Roblox made, I currently have no idea where to start or what to learn, please suggest what I should learn to script Horses in Roblox, it would greatly help me.
If there aren’t specific tutorials for what you’re looking for, there is precise information, officially made by Roblox, on the aspects you will need.
This information can be found in Roblox’s Creator Documentation.
For movement of the horse:
(you won’t need all of these, probably only a few, I put them all here because some are slightly different and you might find one better to use than the other)
All of the above replace the legacy BodyVelocity, BodyGyro, etc.
For getting player input and being able to ride the horse:
For use of tutorials if there are no new ones:
Try looking for tutorials that are similar to what you want but not exact, for example a spaceship, or a boat tutorial.
This is because they will likely use similar properties to horse riding, like with AlignOrientation, with few differences, so it can be useful to learn from those, and just remove / change what you don’t need, for example being able to float.
Footnotes:
It might seem like a lot, but these kinds of things you only need to learn once! Good luck 
don’t hesitate to ask for more support in future.
Also, your English is good, very clear in your post. 