Long story short: The idea of subscribing to feeds is that you have one place to go (your feed reader) to see if any of the subscribed pages/blogs/lists/etc. have changed or updated.
Your feed reader will periodically poll the subscribed sites to see if there are any new posts/articles that you want to be aware of.
For instance, I subscribe, via RSS feeds, to a large number of blogs. This saves me from having to type in a 100 different urls each day to check for new stuff. Instead, I just check my feed reader -- it'll tell me if anything new has popped up.
.Net is not necessary to read feeds. It may be necessary for some feed readers, I suppose. I tend to use bloglines or google reader as I prefer web based readers. They work from any machine I happen to be using.
Does that help?