Please confirm if you have SharePoint Foundation 2010 or SharePoint Server 2010. This feature is not available in SharePoint Foundation 2010.
If you have SharePoint Server 2010, it depends on the template you used to create the site collection. Some of the templates do not by default activate the site feature
Office SharePoint Server Publishing Infrastructure. If this is not activated then you will not see the navigation under look and feel. To enable the feature:
If you are not at the root of your site, under Site Collection Administration, click
Go to top level site settings. On the Site Settings page, under Site Collection Administration, click
Site collection features. On the Site Collection Features page, next to Office SharePoint Server Publishing Infrastructure, click
Now the navigation link should show up under look and feel.