Let’s take an example of adding a lightning component on Account's lightning page layout -

  1. Switch to lightning experience.
  2. Go to any of account's record > click on setup (gear) icon > click on the edit page.
  3. Search lightning component - MyOpportunities or you will see the component in the custom section on the left side menu.
  4. Drag and Drop the MyOpportunities to desired section in the lightning record page > save > activate the page, if not already.