Inkscape is reasonably easy to use and has a wide range of capabilities - I use it to make posters and figures. It is also good for converting images from raster to vector format.
In the session I essentially just ran through its basics, with examples. An introduction can be found here.
The best way to learn it however is to play around. Answers to almost any Inkscape question you might have can be find by googling it - the program has been around for a while and is very well documented.