Integrating gitlab with jenkins

I have followed the documentation here and yet to get the integration with my jenkins to work

the username and password fields are those login to the jenkins server?
I have filled the correct login information but still does not work.

Also am not sure exactly what this integration does exactly. I mean if i already setup the gitlab plugin in jenkins and have added my API token, what does this jenkins integration form do exactly?

Anyways when i fill the from in screenshot above i still get failed and not sure what is going on