how do I block shopping websites like amazon, Macys, anything shopping related only?

There is no setting that will block all 'shopping' websites.

I'm not trying to make any assumptions on whether this if for a child or not, this is just one method of blocking website access.

You can use Parental Controls in Screen Time to prevent access to individual sites (such as Macys, Amazon, etc..) but you'll need to list these out in a "Never Allow" list. Or alternatively, you can create a "Always Allow" list so you can only access those particular websites. Everything else would be blocked.

-> Use parental controls on your child's iPhone, iPad, and iPod touch - Apple Support