Thumbnail troubles

So I’m trying to get a thumbnail next to my posts but i’m new to all this and don’t get all of the code

the thing is that it stands on the right side of the post title.
1. in the FAQ it says to add the code in the styles sheet, is there a specific line on which it needs to be placed?
2. is it possible to make the top of the thumbnail be at the hight of the first line of the excerpt?
3. Which picture does it take for a thumbnail, the featured image?

Thanks

http://wordpress.org/plugins/list-category-posts/