Login to your Blogger Account.
Go to Dashboard, Edit Layout, Page Element.
Add a Gadget, and Add Feed.
Enter Feed Url :
For Recent Posts : http:// blogname.blogspot.com/feeds/posts/default
For Recent Comments : http:// blogname.blogspot.com/feeds/comments/default
Make sure you replace blogname with your actual blog url.
You can change the title with Recent Posts and Recent Comments.
Save and Done.
Note: Sometime you need to wait a longer time until the posts or comments appear.