Comments are one of the best way to Know whether Audience is liking your blog or not and through comments you will be able to know where your user is getting trouble and then you can help him. Comment is the best way to contact with you audience and sort out most of their problems.
Follow the Following steps to Enable the Comment box in your Blog
Step 1: Go to You Blogger Dashboard and select the blog from which you want to enable the comment box.
Step 2: Go to the settings section, in settings section select the "Post and Comments" Option.
Step 3: In the Post and Comments Section, Make the Comment Location "Embedded". In who can comment , select anyone(recommended) and Turn on comment Moderation as you will be able to moderate comments by your users. Show word Verification and Backlinks are options of your choice, i will recommend you not to use word verification because if you will make it on then some users will get difficulty while commenting which inturn will decrease your comments.
Follow the Above Steps in Reverse Process in order to Disable the Comment Box from Your blog in Blogger.