Good for you fella!! If you can come across and old tree trunk rotten inside, you have a hive. It's one of the oldest ways of keeping bees and good for a start.
You should carve end caps and make an entrance hole, bees live as they would in nature but when you need honey you open up from one end and just take what you need.
I made 3 hives like that with my friend, but no bees there yet, only mouse. I got 3 regular hives out and 2 of them had bees starting to live there, unfortunately one got a sickness and died out during the winter. Anyway I was using some old hives and by the looks of it, they might have seen too many years of service. Making a hive by yourself can be a challenge because of the precision it requires. Red has done an incredible job on his hive, really well finished hive. I still have to cut up wood for my hives, so no experience there....
If you'd be interested in trunk hives, I could give you more detailed info. Anyway, very well done and best of luck!