Hi, In my opinion...the best way to get a good overview of the system (if you don't work with it every day as a user, don't have access to training and don't want to read a ton of manuls) is to create a company in GP (use the set up lists) that sells items of stock, and then invent a weeks transactions and try and process them. ie. First set up some GL accounts - Bank, Debtors control, Creditors control, stock, sales, cost of sales, sationery, insurance, etc. Then buy some stock from a supplier (place a PO and print it out, enter a receipt of stock, and then enter the vendor invoice), sell some of this stock to a customer, get paid by the customer, pay the supplier, buy some stationery on a credit card, process your ficticious credit card statement, pay the credit card bill, process an invoice for insurance and pay it, reconcile your bank, find some stock in the warehouse is missing and write it off..etc etc.
If you build up a scenario like this and then try and find out how to account for it in GP, you will learn more than reading a whole load of manuals in isolation. Plus, GP will force you to complete any set up tasks you haven't done..like creating item sites, sales prices, vendors, functional currency, financial periods etc etc. Only use the manuals / help file when you are trying to understand a particular issue.
Post any issues you are having here, or if help files don't explain things very well.
You could always attempt an exam. The study manuals for these are quite good and force you to look into the application to fully understand...but get your hands dirty as above first so you have a good idea of how the whole system hangs together.
Start with just the minimum standard modules Financial and Distribution. When you crack these (and there is an lot in them) you can start to look at project accounting, field service etc. and other bits of functionality like analytical accounting or whatever.
Best of luck.