I bet somebody else has explained this before 😀 . If you want to follow a fellow WP.com blog you just have to click the follow button (login to your WP.com account first), and their post will show up in your Reader. But what if somebody you want to follow has a different blog engine? Don’t worry apperently you can follow about any site from your WP.com blog Reader.
1. Click on you reader menu you need to login to your WP.com account.
2. You will find the reader page. You have ‘Blogs I follow’ click on ‘Edit List’
3. Copy paste the URL of the blog / website you want to follow, then click follow
Open by your Reader once in a while to find out what they are up to, I don’t know what will happen if you copy paste a Facebook account, but i’ve tried blogspot, blogger, WP.org and they seem to be working fine.