Jekyll uses Markdown-formatted links, but how can I link to internal content?
[[link]]
There are multiple ways of linking in Jekyll, some of which are now outdated.
The recommended way to link to internal files is
[Link]({{ site.baseurl }}{% link path/to/file.md %})
Note that this will cause an error if the file moves or gets deleted.
To link to a page without causing errors (broken links instead):
[Link]({{ '/path/to/page/' | relative_url }})
Note that here you need to know the permalink of the page and pass it through the relative_url filter to ensure that it is prefixed with the base url of the site.
The permalink of a page depends on the permalink setting in your config file and the permalink key in the front matter of the file.
If you want to use relative paths (and want the links to work in GitHub's markdown view), you should use jekyll-relative-links. This lets you write links like:
[Link](./path/to/file.md)
[Link to file in parent folder](../file.md)