passing user ids

All:

I am in the midst of adding an ‘online mall’ to my site where i will share a portion of my commission with my users. To do so, I need to have a means to add the user’s log name to the link I am using.

I have done this previously on a self-created website by naming and passing a defined variable to the link itself. I did this in my header.

I think the same process should work in wordpress, but I am unsure as to which file would allow me to do so.

Thanks in advance!