It has not been called "Sage Line 50" for many years now, it's just "Sage 50 Accounts". Sage 50 Accounts and Sage 50 Payroll are separate applications.
Yes, you really need some familiarity with basic bookkeeping principles to understand it, but that is nothing you cannot pick up in the space of a few weeks. For the more advanced stuff, Sage does offer pretty good support.
What sort of job role are you looking at? Normally a bookkeeper or accountant would be using Sage and I cannot imagine you'd apply for such jobs without basic experience in those areas?
You can teach yourself most of the core functionality of Sage Accounts with a copy of Instant Accounts, which will be cheaper. They are actually the same application, Sage 50 just has more advanced functionality such as multi company support etc.