Getting user id when they click on a link or view a page

Hi guys,

First of all I’d like to mention that I am as green as they get when it comes to building a blog or website, so pardon me if I don’t understand what you are saying.
As for my “problem”: I want to register the user ID of whomever clicks on a link I post or visits a page I created. I know it can be done by implementing some sort of HTML code, but I don’t know how to set up such a code. This is basically what I want to create:
Get (User ID) when viewing (or clicking, whatever is easier te set up) (pagename).
I know this is possible, but I have no idea where to begin. If someone could help me with this I would greatly appriciate it.

Greets,
IQ