Create a product and click Manage in the Sales Channels area in the upper right.
Make sure the Buy Button is checkmarked
Select 'MORE ACTIONS' in the listing top menu and in the dropdown click
Embed on a website
Once the dialog box pops up you can copy the embed code or select
'Preview and customize' to change the look of your button
Go to your page template you are placing the Buy Now button on and open up the "EMBED SHOPIFY BUY BUTTON" widget. Replace the demo code with your own and click Save Widget.