Google Docs offers the ability to create a Table of Contents for your document, and in the most recent update they now let you use page numbers.
To create a Table of Contents, click where you would like it in the document then go to Insert - Table of Contents and choose either the option with page numbers or the option without.
Your document Headings (Format - Paragraph Styles or by clicking on the dropdown by Normal Text on the toolbar) will determine your Table of Contents layout.
If you use Heading 1 for one topic, and Heading 2 for the next topic it will place the second topic as a subtopic of the first one on the Table of Contents. The same follows if you were to use Heading 2 and then Heading 3 for the next, etc.
To refresh your Table of Contents, click in the Table of Content box and then on the refresh button to the left of it that will appear.
Example of using the different headings and how the Table of Content then shows them: