How to add a blog in MyYahoo:

Step 1:

Click on Add Content

Step 2:

Don't enter the address in the wrong place. I did it here. This is the "Find Content" box. You want the "Add RSS by URL" box. Click on "Add RSS by URL"

Step 3:

Paste the web address of the blog you want in My Yahoo here. and click add. A confirmation dialog will appear and if you can subscribe. Click yes and the blog posts will appear in MyYahoo.