I am currently writing an app. First time. Learning as I go along. There's quite a lot of learning involved. If you don't want to write it yourself you can hire someone to write it for you, just as you can with any programming or web design. There's various sites where these services are offered.
BTW, I think if you have to ask in a domaining forum if there's a place online that shows you how to make an app, you might be doomed to failure as finding readily available information is the easiest thing you can do.
Good luck.