How do I use rss to place a blog feed from another blog to my own blog?

I simply do not understand how to perform this simple task and no matter how many times I read about really simple syndication it doesn't become any clearer!

A friend of mine put a blog feed for me onto her site, but can't tell me how to do the same in return. Links are great, but the feed she put up for me was something else.

Can anyone tell me the really really simple way to understand how to do this please?

see also

Social Network Marketing

There's no simple way to understand something that's complex. It involves javascript, php ... computer programming.