Now the ATO must obviously have input from Accountants when it comes to terminology and legislation- can't have things too simple now can we- accountants would have no work then.
ATO has made BAS terminology unnesessarily confusing for the lay man- I struggle and I was an accountant (in a previous life so don't hold it against me ..lol)
The BAS return is split into sections:
One where you calculate GST related information....
In this part you do not enter Share Sales, but only Profits on Share Sales- it's largely irrelevant anyway if you make a mistake because there is no GST on Profits (however bear in mind that what you declare here as profits is matched with details in your final Income Tax return so don't stuff it up)
There is another part for PAYG- Pay as you go Installments, this is where you enter in the Share SALES and calculate your PAYG Installment for the 3 months based on a % the ATO gave you. They calculate the % based on the % tax you paid on the prior year income tax return expressed as % of sales. You can vary this amount under certain conditions, if e.g you are making less profit than usual snd estimate that this is going to continue for the year. The ATO website provides guidelines as to when you can do what
Don't be daunted by what you read here, the BAS form is simple and the ATO provides usefull guides to completing them.