l (as in "L") is first two letters of race's name, all lowercase (case sensitive). Easy to remember, just look left.
c is entirely optional and may be omitted. If c has a value (anything other than whitespace) then it disables the category line on the template being called. This allows the use of these templates without having them categorize the page they are called on, if this behaviour is not desired. (Note that this parameter is part of the original plink templates, so the parameter may be used on those separately if so desired).
What it does
It compares the string input for link to its own values, then spits-out a template call to the much longer-named faction templates.