Hi @sufyan.maqsood and welcome to the forum,
It depends on how comfortable you are with the various aspects of web development/anvil.
If you’re new to anvil and web development, start with the functionality of anvil - follow the tutorials - flesh out the logic of your e-commerce app and then worry about the html template later. Get to minimum viable product before worrying too much about the aesthetics… Play around with some of the css/roles in theme.css to adjust specific aesthetics to your preference.
If you’re new to anvil but comfortable with web development I’d still suggest the above approach.
If your comfortable with anvil but new to the idea of building custom templates I’d start by adjusting the standard-page.html and break it/rebuild it and get a feel for how the docs relate to anvil’s own custom HTML template (which standard-page.html is an example of).
I’d also check out the ticketing app from the anvil Blog, which is an example of a fully customised set of html templates for an anvil app.