You can start by just asking a horse to take one step forward and one step back. Think about doing this with each foot, all the way around. Eventually you can place each foot anywhere you want it with your reins, a very useful skill.
If it helps to have a visual aid, you could draw a circle in the dirt and place one foot in the circle at a time. For the photos below, we've used a round piece of wood.
When asking, try to be as light as possible and offer a release, a reward, as soon as the horse makes the slightest try. So you might ask for a step forward and then release any pressure as soon as his leg muscle twitches to start to lift up a foot. Or you could offer a release from the start to get the movement you desire.
You wouldn't worry if you got two steps at first, or the horse is a little confused. Just start over again and adjust your presentation so that your horse can clearly understand what you want him to do. The better your timing gets, the harder your horse will try to figure out what you want and your horse will gain confidence.
This should be something that is low key and fun for you to do any time you are around a horse. It is an easy way to check in with your horse and get "with" each other before moving onto something else.
Once your horse is pretty clear about what you mean (want) by what you do, you could experiment with different obstacles. Just keep in mind that you want these exercises to be fun and constructive.
Now this gelding is being asked to explore stepping up on a pedestal. That could help him with trailer loading and trail obstacles in the future. There is no rushing in letting him explore here.
It could even help a horse understand the purpose of a hoof stand
Horses of all ages can do this
two feet, three feet
three feet, four feet
loading up in the trailer
stepping up on a rock, stepping up on railroad ties
stepping up on a big log
all four feet up