JustShop theme has a custom Page Template called 'Blog' included in order to show the blog list on site.
Of course, you need to create at least a few posts from Posts → 'Add New'.
Then,
create a new page by going to Pages → 'Add New' and select "Blog" as
its Page Template from right bottom side as seen in Page Attributes box.
See screenshot below.
This newly created page will now display a list of the Posts (as you can see in demo).
Tip: You should have this Blog Page as a menu item in the main navigation menu.