GTK newbie questions: using "What's This" and using Yelp

[Neil Zanella <nzanella gmail com>]

Hello,

I am a GTK newbie. I'm porting an application I wrote in Qt to GNOME/GTK+.
I've constructed my UI with Glade. Now I want to add "What's This" feature.
I don't know how this is done in GTK+, and don't see anything that supports
this in Glade, but I see that the Gimp has it (yeah, I could look at the GIMP
sources, but perhaps someone on this list already knows the solution).

Also, I would like to integrate my DocBook documentation sources with
yelp, and have my app invoke the yelp system/application. How should
this step be done, given I plan to write a GNOME app?

Thanks,

Neil