Hyperlinks continue to be central to navigation on the web, such that not adhering to best practices can break the usability of your site or app.
Links (originally called "hypertext links", then shortened to "hyperlinks", and now typically referred to just as "links") are the original way of navigating from one page to another on the web. They are ubiquitous on the web and common in web applications and web-like desktop apps.
Their strength lies in their simplicity. They can be embedded within blocks of regular text, allowing them to be read in context without interrupting the user's flow, while also indicating that content related to the linked text is available.
Additionally, as long as they are implemented correctly, they offer the advantage that they don't need much decoration to invite action (like buttons do). This is because they are so standard that users expect to be able to click on text that has a distinct color and/or is underlined.
Wikipedia is a showcase for the use of links:
Links can be used within chunks of text to indicate the presence of related content, but can also stand on their own to attract more attention, such as for primary or secondary navigation, as in breadcrumbs, menu bars or vertical navigation.
Hyperlinks, when used to navigate between or within pages or screens, are familiar and easy to use (with a mouse or keyboard, at least), so they can be used liberally. Although having too many redundant links on a page can reduce usability.
As described above, it is important to have a distinct default link style and a separate style for visited links.9 The other link states are "active" and "hover". But note that hover is not available on mobile devices, so don't rely on it.
It can be helpful to indicate links that go to external sites using a small icon, such as the one below.