Tumblr: How to Add Comment Functionality
One of the easiest options is to install disqus in your tumblr.
i. Go to http://disqus.com/ and create an account
ii. Log into http://www.tumblr.com/customize and click Appearance
iii. Add your disqus shortname
iv. Voila, you're done! (Just remember to add your disqus shortname every time you change your theme)
If you can't find the Appearance menu, that means your theme does not support the function and you could add it manually.
i. Go to http://disqus.com/ and create an account
ii. Log into http://www.tumblr.com/customize and click Appearance
iii. Add your disqus shortname
iv. Voila, you're done! (Just remember to add your disqus shortname every time you change your theme)
If you can't find the Appearance menu, that means your theme does not support the function and you could add it manually.