How do I promote my store or Patreon on a page?

Add the Promo block, in the Common section of the block picker. It puts pictures on one side (up to four, each with an optional caption like a product name and price) and your pitch on the other: a heading, a line of text, and a button. The button can point at a page on your site or an outside site like your merch store or Patreon.