Hi @barrymac20 ,
Two years and still learning . .
Seriously, it depends on two things - what coding experience and data structure understanding you have to translate this and the time you are prepared to spend at times learning some of the unique ways Power Apps does things.
I have an Access/SQL/VBA background and I struggled for a while at times doing things the "hard way" until "the light bulb came on".
I also spent a lot of time watching YouTube videos and duplicating things I had not already done. This is not an exclusive list, but start with Shane Young @Shanescows and Dave's Tech Tips. There are also many other useful authors (in no particular order), Reza Dorrani, Daniel Christian, Chino does Stuff, Pragmatic Works, Todd Baginski & Paul O'Flaherty.
To answer the question as to what they are for, in my case, users work on maintenance of power line infrastructure and most are field-based. The apps both field and office manage this process from end to end including all data collection, reporting, photos, documents and quality audit. It is also shared with our customer giving them a real-time view. About 30,000 jobs have been managed with this process. We use a SharePoint back end.