Selecting this option will automatically generate an example project with preset pages - Help Center article and Landing page. You can play around with them changing content, adding or removing the blocks.
To go with the quick start, select Start with an example option in Welcome to Compose screen. Compose app will open with the All pages view. You will see automatically generated pages: Help Center Article and Landing Page. Go to each of the pages, view and change (if necessary) the blocks and start filling them with content.
If you want to add another page type or have more field types in the existing page, you can do that by updating your content model in the Contentful web app.
To extend your existing page type with more fields, access the relevant page content type in Contentful web app in the editing mode and add and configure fields to it according to your preferences. For more information, please refer to Creating page content types.