If you have two PCs you can easily play together. At least with Java Edition. One of you just has to make their game available in LAN. Then the other should be able to find it in the multiplayer menu. That way you don't have to make a Minecraft server. Been a while since I've done that so I can't remember what everything is called.

My kids started in creative mode without any monsters and just built stuff. In time that expanded in complexity. Sometimes inspired by YouTube videos.

Eventually they started playing on community servers. When your kid is at that point definitely talk often with them about the dangers of online life, privacy and so on. Minecraft servers are not as bad as Roblox servers but you still have to watch out. My kids already met some trolls who destroyed everything they had built.