Don't worry, my kid he has autism and it took him until he was about 7 to fully grasp and potty train. For starters, it is best to start potty training at about 1-3 years old or when they are about that way they can grasp it and understand it a little more.
I would honestly start with a little potty and try sitting them on it so that way they can get the feel of the potty.
One thing you can do is kind of figure out their potty schedule and try to get them to go on the potty. Another thing you can do is try rewarding them for pottying and getting them to go in which this kind of worked with my other two.
Another way was we kind of skipped the little potty training potty and went straight to the big potty and that worked too but there could be a chance your child is scared of the potty and will need comfort and a lot of talking through.
But as always you know your child better than anyone and if they are not ready to potty train then it is okay. Don't beat yourself up over it, it just takes time.
Potty training potties, toilet seats and stairs here!