You can set the height for RecentFeatures via its block options. If you want to force a certain width...
Code:
#recentFeatures { width: 800px !important; }
Put that into
EXTRA.css, and change the width to whatever you would like.
An article is simply a thread on your forum. XenPorta turns it into an 'article,' of sorts. When you select the nodes you want your news to feed from, those threads become your articles. If you want, you can enable the article view for threads, like Jaxel has it on his site:
http://8wayrun.com/threads/soulcalibur-lost-swords-beta-test-announced.17282/
Or you can just have the title redirect to your thread. You can toggle this in the XenPorta options.
But, to put it simply, to create an article, all you have to do is post in one of the nodes you've selected for the RecentNews block to feed from.