Internal links are referring from one page to another page on the same site. It helps the online visitors easily navigate your website and, also Internal links pass the page authority on the same site, so internal links help SEO to get a better rank on the search engine
How Internal Links Works?
What are the Important Factors on Internal Links?
External links are referring from one website to another website. External links improve the site trust and increase the site traffic so external links help SEO to get better domain authority.