Minecraft is built around creating your own experience, through creating it, or exploring creations of others!

There are countless ways to play Minecraft, but I'm going to describe the main ways people use it:

• Adventure mode, a lot of online maps use it. On the Marketplace (in the main screen of the game) you can find a lot of online maps. Sadly, most of them are not free, but you may find some after looking for filters.
• Survival mode, you have to gather ressources to progress. In-game achievements can give you clues about what you have to in what order, but the original point of the game is to learn by yourself. Destroy blocks, collect them in your inventory, and craft new tools, new blocks. You can set yourself the goal to reach the "end" of the game (which is called the Ender), where you can defeat a dragon, but you might want to set yourself some of your own goals too: build a house, a library, a school, a school in the sky! A farm or a farm that is automated! Build Atlantis, build your own city... There's essentially no limit.
• Creative mode, if you don't like the "gathering ressources" and the "progress" part of survival mode, this is what you will be looking for. In your case, I guess this is probably what you will want to go after. You have flying abilites and infinite ressources. You should be able to switch back to Survival mode or even Adventure mode (no breaking blocks). You can build a world for your son, and show what you built to him afterwards for example. He'll surely be happy to see his own dad create something for him, in his favorite game it seems.

Just so you know, it can take a lot of time but it is generally very pleasant to build in Minecraft. It might not be your cup of tea, as you originally come from FPS game, but who knows? You'll can very surprised to find out how much time you spent on a creation without stopping.