A lot depends on the application programs that your employer uses on the AS400. There are many different applications available and they can be very different in the way that they work. For example, some applications will update your data when you press the enter key, while others will require you to press a function key to update.
Most AS400 applications are quite logical in how they work – for instance you can’t enter a sales order for a client which has not yet been entered in the client database. Some applications also have help text available (usually displayed if you press the help key or F1).
Maybe if you let us know the name of the application software there will be someone here with experience of using it.