It really depends on the industry, the company , and so on.
You have to get in and ask questions, look at the code, the designs, ask reasons why and why not certain things are done. The banking industry does certain things, manufacturing companies do certain things, and so on. Every one does something a little differenlty but banks have certain formulas, rates, calculations that become standard and the more you learn about it, the more in demand you'll be. Same goes for the other industries.
The only way you can really know the ins and outs of different systems is to get in, learn it, ask questions.. Basically experience and mentoring.
I've worked on systems that tracked dangerous materials. The system needed to track the material in real time down to less than a millisecond because if something was left out of a certain storage facility for a short time, there would be major major problems. If it were out for only so long, then it could be ok. There were calculations on time, dates, storage, temperatures, vehicle speeds and so on. Things were tracked using RFID, barcodes, and the web. It was a complex system but i learned
alot from it, even though i was more involved in the web application and design then in building what backend of this system.
I worked on a government system that basically build the "highways in the sky". A system where everything had to go through a billion different approvals.
I worked on smaller inventory systems. I worked on various web applications.
Everything is different, but when you learn how systems are built, how certain industries do certain things, laws of certain industries, how to use certain formulas, calculaitons and so on you become somebody people need, rather than somebody who just knows technology.