To add the product widget to your site, please see the following guidelines;
Go to Online Store in your dashboard
Click on Customize
At the top of the page, select Products
Click on Default Product or it's equivalent (what you have in your store)
Here, there are two steps involved. You can decide to add the widget as a block or as a section. You can learn more about them here: https://help.shopify.com/en/manual/online-store/themes/os20/theme-structure/sections/.
For me, I'd prefer to add the product widget as a section so that it stands on its own and is nicely laid out on the site.
So the next step would be to click on add a section
Then choose the product widget
Once clicked on, it will load on your site like it shows below.
Remember to save your work
If you're using a block: Follow the steps below
Click on add block
Select Product Widget
This is how it looks like when added as a block in the product information section. It takes the structure of all blocks in that section.
You can decide to move it up or down depending on your preference by clicking on the drag and drop icon
Remember to save your work.