To link files in the same directory:
ln notes circular
This creates a link circular to the file notes in the current working directory.
To make several links to a file in different directories:
ln part1.txt ../helpdata/sect1 /public/helpdoc/part1
This links part1.txt to ../helpdata/sect1 and /public/helpdoc/part1.
To use ln together with special pattern matching characters:
ln project/*.xdh $PWD
This links all the files with the extension ".xdh" in the sub-directory project to the current directory.
The value of the environment variable PWD is used instead of giving the path to the current directory.