Google exists to serve the searcher. That means Google is constantly trying to determine which results are most relevant to any given searcher and any given time. In addition to relevance, Google considers credibility too. So the search engine looks to see if other websites have linked to yours. If so, that means your content is worth linking to and is, therefore, more credible when compared to a website not linked to externally. In a nutshell, link building is what SEO professionals do to try and get links to their websites in order to improve search results.

Page speed refers to how fast your site loads for a user, something Google takes into account while ranking websites since a faster loading page directly translate to better user experience. If the interviewer asks what you would do to increase page speed, describe how you’ve achieved this in the past with examples such as reducing image sizes, enabling compression, reducing redirects, removing render-blocking JavaScript, leveraging browser caching, improve server response time, using a content distribution network to compress files, optimizing the code, etc.

This gets back to the question about the factors that are outside of your control. On-page SEO includes the factors you can control, such as keywords, content, page structure, internal linking, load time, etc. Off-page SEO includes those factors you can’t control, such as backlinks.

Nofollow links exist because we don’t want every single webpage or link to be something a search engine crawls and ranks. Therefore, no-follow link attributes tell search engine bots not to follow a certain link. The link is still clickable for a user, but not followed by a bot. On the other hand, all other links could be considered do-follow links, even though they don’t have to have special attributes to tell the search engine bots to follow them—the bots will by default.