This template links to one person's accounts, here and on two other Wiki-projects.
There are five expected parameters, which may be named or just used in sequence:
User= The username (without the "User:" prefix) on this project.
Project= The name of the first other project.
Project2= The name of the second other project.
Alt= The username (without the "User:" prefix) on the first other project. (This is only required if different from User=; it can be omitted if the same username is used for both projects.)
Alt2= The username (without the "User:" prefix) on the second other project. (This is only required if different from User=; it can be omitted if the same username is used for both projects.)
If you want to omit the 2nd other project, simply use Project2= and Alt2= (end of field, no value provided).
If you also want to omit the 1st other project, simply omit the second through fifth parameters.