Bubble lets you customize how your app looks on social networks when users share a link to your app. The SEO section of the Settings Tab also lets you tweak SEO settings to improve visibility by search engines' crawlers.
Popular social networks let you customize how links to your website, when posted on their platforms, look like. You can control this settings (open graph meta tags) in the Metatags section. You can customize the image, and the content of the text that will be displayed.
Here is what these settings look like for the bubble.is site. And how this looks on Facebook. Note that defining these settings in the Settings Tab will be applied to all pages of the application. Bubble also lets you modify these values at the page level. This is in particular useful if you want to use some dynamic information (for instance, the current page's product's image) instead of a generic image. If you have some settings at the page level, they will prevail over the application's settings.
Bubble lets you customize how your site is seen by search engines' crawlers. These are advanced settings, and should only modified if you know precisely what the consequences of these settings are. A wrong setting can significantly change your site's raking on search engines. It is important to keep in mind that search engines are very secretive about what makes a high ranking.
If you check the box 'Expose the type of tags for text elements', you'll be able to define some elements as 'h1', 'h2', 'h3'. It'll be your responsibility though to make sure you're not doing something weird there, which could harm your indexing.
The robots.text file (see example) provides some instructions to search engines' crawlers regarding the pages to ignore when indexing your site. Bubble exposes a robots.txt file for all apps. By default the development version of your app isn't indexed.
If you want to customize the file, you can check the 'Customize robotx.txt' box and overwrite the file content.
The sitemap file is a file where you can list the web pages of your site to tell search engines about the organization of your site content. Search engine web crawlers read this file to more intelligently crawl your site (see example). If you want to expose a sitemap, you can check the 'Expose a sitemap file' box and pick the pages that should be shown. This will update robots.txt to point to the sitemap, and will generate the sitemap.
A 301 redirect is a permanent redirect from one URL to another, which transfers most of the ranking value to the new URL.
At the bottom of the SEO section, you'll be able to enter old URLs and new URLs. Note that the URLs should be the full URL (including the protocol) and it shouldn't be an existing page in your app. For instance, if you have a page on your app appname.com/page1 and if you define a redirect for the URL appname.com/page1/something, the redirection will not happen.