How do i put in user id in a banner

I would like to know how im gonna put in a user id in a banner.

For example. I have 5 logged in persons on my page, and 3 of them has clicked on the same banner, but I need to know who is clicking.

My affiliate has this banner and told me to put in &uid= in the link, but I want to automatically put in the user id after that.

Here is the link, where I placed the &uid= as I was told. but what should I write after that, so it would show the user id on my affilates page, when maybe user 5 and user 18 is clicking on the link.?

What to do.