Shopify Buy Buttons are displayed on your site through the use of the installed Shopify Product block. The cart on the other hand is automatically displayed when required.
The way you place Shopify Product blocks on your site is up to you - you may wish to place multiple on a page, create individual pages for products, or simply place the blocks within existing content.
There are three key ways that Shopify Buy Buttons can be displayed on a page:
On install you are given an option to 'Automatically Configure Page Type and Products Page'. Selecting this option will set up a Product page type, with attributes and default blocks. You can either use this configuration as is, or customize it further to meet your needs. This option works great if you wish to manage and display each of your products as a separate page, with product information and selection entered via a composer driven page.
The adjustment of product details such as prices, stock levels and cart thumbnails is performed through the Shopify dashboard. Similiarly, the configuration of shipping options, payment options and other order related aspects is peformed with the Shopify dashboard.