Adding Your First Item
Tracking something takes one product page URL and nothing else. There is no account to create and nothing to configure first, so the fastest way through this page is to have a product page open while you read it.
What you need
A link to the product page, and that is the whole list. No account, no email address, no subscription to begin.
The free tier covers five tracked items. That is a real limit rather than a trial that expires: five items work indefinitely, and nothing you have already tracked stops working if you decide not to buy Premium.
Adding it
Paste the URL into SmartTracker and it loads the page and preselects the number it takes to be the price. That second part is the one people skip past: a product page carries several numbers, and you can change the selection if it picked the wrong one.
Whatever is left selected is what gets followed from then on, so a shipping cost or a crossed-out list price left in place by mistake is what you will be told about later.
What happens after that
SmartTracker re-checks the page on its own and records what it finds, building the history the chart draws from. You do not need to keep the app open, and on iPhone and iPad you do not need to leave it running.
Nothing you track leaves your device, which is why none of this needed an account: your items sit on the device and sync through the iCloud account you already have.