Anchor text is the visible, clickable words of a link. It matters because it tells an engine, and a reader, what the page on the other end is about before either has visited it. A link that reads pricing tells an engine the target is about pricing. A link that reads click here tells it nothing.
Use descriptive anchors that name the target. They help ranking, they help a reader decide whether to follow, and they help an AI understand how your pages relate. This is part of why contextual links in the body are worth more than a generic nav or footer link: the surrounding words and the anchor give the link meaning. See internal PageRank.
Do not stuff the same exact keyword anchor into every link to a page. Natural variation reads better and does not look manipulative. And never hide that something is a link. If it is clickable, it should look clickable.
Topkay's linking tools read your internal anchors and flag links with empty or generic anchor text, where you pass a page along with no signal about what it is.