Because links are a fundamental part of Twine stories, the way they are written is shared across all story formats. In short, you create a link by placing two square brackets around text in a passage.
[[A passage]]makes a link to a passage named "A passage".
[[A label->A passage]]also makes a link to a passage named "A passage", but the text that is displayed onscreen is "A label".
You can also reverse the arrow direction and write
[[A passage<-A label]], which has the same exact effect as the previous example.
Passage links are case-sensitive. That is, a link to a passage named "A passage" will be treated differently from a link to a passage named "A PASSAGE".
Passage links are represented with a solid line ending in an arrow in the story map. A passage that links to itself shows a circular arrow. Story formats can extend Twine to add references. You should check your story format's documentation to find out how they work. You can also disable story format extensions to prevent these lines from being drawn.
When you create a new link while writing in the passage edit dialog, Twine will automatically create a passage for you with the correct name after a short delay, if it doesn't already exist in your story.
Twine also tries to detect when you're starting to write a link and opens a list of possible completions. To accept a passage name in the completion list, click or tap it. If the suggestions don't include what you want, or if you're creating a link to a new passage, keep typing and the completions list will disappear.
If you change your mind about a passage name, you don't need to manually edit links in other passages. When you rename a passage, Twine will update links to passages for you. It won't, however, update any references to a passage that use story format-specific functionality, like code.
It's possible to use more than plain text as the trigger for a link, but how
this works is dependent on the story format you are using. It's often possible,
for example, to enter an HTML
<img> tag in the label part of a link. But this
may or may not be supported by the story format you are using.