I put a picture on line
http://imgur.com/a/K1yry

the fonts on my screen are not that slender, they are awkward, ugly, I
don't know

What can I do to make them better ? Which font should I install and how can
I instruct the Gnome desktop to use them ?

In Fedora there's a thing called "Fedy" that automagically does a list of
things and one of them is making fonts smooth

But I have no idea how it does that, it's a cute tiny window and I just
click a few buttons in it.

So any suggestion is welcomed

Thanks in advance