To link to a section within a page of your Google Site you need to include section headers. That's easy to do. To include a section header simply insert one of the layout options listed in the right-hand menu of the Google Sites editor. Then just type a title for your section. Then when you publish your site you'll see a link appear when you hover your mouse pointer over that section title.
Watch this short video to learn how to link to sections with the pages of Google Sites.
Applications for Education
As I mentioned in the video, linking to a section within a page in Google Sites could be helpful your students when you're trying to direct them to a specific resource within a long list of resources on a Google Sites page. You could post the link to the section in Google Classroom or any other LMS to direct students to a specific resource or section of a resource list.