Internal links are those that point from one page to another on your site. There are two internal linking strategies for your website that you should consider.
First is a linking strategy with the site visitor in mind, and it's fairly simple. When adding content to your website, determine whether there are other pages or posts that should naturally be linked within the content. This could be content that guides the visitor to the next logical piece of content or provides context.
Second is your internal linking strategy for SEO. Using optimized internal links is a surefire way of allowing Google to regularly discover relevant content on your site. An additional benefit here is that internal links can help to demonstrate the contextual relationship between two pages - it sends a signal that page a is related to page b. If you don't show Google how your content is connected, your users won't make the connections either.