The Pricetag part of the prac is unfortunately cancelled. They have upgraded their system and our shopping cart does not have a module for it. The did us a favour by allowing you the experience, so we have no say in the matter, except to wait for a new module to become available - or to code it ourselves. That will take time, of course.
If it did work, you would have gone to an admin page at Pricetag, which they supply based on your account settings, where you would configure your account, as shown in the tut letter. The rest happens automatically. In real life, you would pay them around R200 per month, and 5% of every transaction.
That is the first step - setting up your merchant account. What happens cart side is that one then simply selects the payment module under Modules -> Payment modules. The rest is taken care of automatically. On check-out the customer is taken to the Pricetag website, which handles the payment. The adavantage is that they are responsible for security of payment etc. You don't keep any record of credit card details etc on your site. Once payment has been effected, the customer is redirected back to the cart where the products bought are then updated in the database, i.e. taken off so that you know exactly what is left in store.
We are dependent on using this cart, since it is open-source and freely available. None of the other online payment modules currently available works from South Africa. Cash on delivery, however, will work, and that is the only option available for purposes of this prac. It is a silly route to follow, however, and not advisable in real transactions.
So if one would like to use this cart in real life, one would have to contact Pricetag and ask them if they have a module available for the oscommerce cart. I know they are looking into making one available - or was going to look into it. The module is normally just copied to a module folder, but some configuration of files may be required.
The thing to understand is that all commercial (i.e. you buy it over the counter)shopping carts more or less works in the same way back-end. So if you can use this one, you should be able to use any other one.