Pages, as the name suggests, are the discrete pages you create for your OLI course. Even though each page doesn't have to be included in your published course (remember, you can create separate organizations with different resources), every page is listed in once place, the RESOURCES tab, which you can reach via Overview (left column) > Resources tab (right pane). If the page is already in your organization, you can click on its title in the organization panel on the left side of the screen.
Click on any page title to visit the page and edit or preview the page.
Pages can include all kinds of content: text, media, interactive activities, links to external resources, etc. You can build these pages using the tools in OLI, or by connecting external resources to your OLI course. We'll explore your options in specific articles.