Hashim has a choice in Wordpress to either show an excerpt of his blog posts or display the whole text. Leo strongly advises anybody with a blog to give away the full text. Some bloggers only make the excerpt available in RSS readers because they may have advertising on the site, but even in that case Leo says to serve the audience first and the advertisers second. Sustaining the audience is the most important thing.
RSS is a way to syndicate content. It means that most websites can create a special file written in XML that contains information about the posts on that site. A reader, such as Google Reader, can aggregate those posts. So if you use Google Reader, or any other type of reader, you add an RSS feed for the blog you want to read (most will auto-detect that), and then you can scan through several blogs quickly. Leo encourages blogs to make the full text available when clicking on that headline in the reader.