question about acrylic painting

[ex-meek386.livejournal.com]

I don't know anything about painting but I'm hoping to try my hand at it and I was wondering if anyone can tell me what it is you use to get the raised lines look that you see in things like this painting:

http://caitlinschwerin.com/gallery.php?gallery=Landscape¤t=951

ETA: Figured it out--GESSO!

And what is the process? Do you paint that medium on first and then paint over it?

Many thanks!

:)