Go into WordPress and create a Post or Page, or edit an existing one that you wish to convert to being a paid access only post.
Once you’re editing, you’ll notice there is a box in the sidebar called ProductPress Products (highlighted below in the bottom right hand corner of the screenshot).
All of your Paddle or Gumroad products should be listed there, provided you've completed the steps to install and configure the plugin.
You can choose to provide access to people who have purchased one or more of the different products from you via Gumroad or Paddle.
Click Publish (or Update) to save your changes.
Now, only people who have purchased that product on Gumroad or Paddle will be able to access that content, and they will need to be signed in to your WordPress site to be able to access it.