You can optionally configure how you provide access to your RSS feed. To do that -
You will see a page with three options for restricting your feed.
If you select this option, anyone can view your blog. You may want to use this option in conjunction with summary feed (hyper link to faq section). This allows you to provide teasers to your viewers through RSS feed which they can consume through popular online and offline feed readers. However to get the full content they will have to subscribe to your blog.
You can select this to let only the subscribers of your blog to see the contents. You subscribers can use most popular offline feed readers to view their content. When prompted for authentication they should provide WordPress credentials (login & password). For example, if the subscriber wants to access your blog feed from any browser (say Firefox) then he will be prompted for login & password to view the feed as shown in the image.
Similarly your subscribers can use most popular offline feed readers like RSSOwl and RSSBandit and some online readers like feedshow and newsgator to access your protected feed contents.
If you click on this option, no one can view your blog, even the subscribed users too.