The steps are as simple as you've said, you simply go onto a plot you think you want to buy and then just plot claim it for 10k.
There are several rules in it however, you have to keep the building no taller than 18 blocks, it has to be sensible buildings that look like a shop so no pixel art, and you have to make sure that what you're selling is something you can stock. Not that it always needs to be in stock in case of something like diamond which is rare, but just make sure you have some every so often is all.