When we create a new blog, we set the Discussion settings to NOT allow comments on posts, as the comments tool is often plagued by spam and can be a security risk. However, the ability to elicit feedback from your reading audience is a very valuable feature of a blog. In order to enable your readers to submit comments on your posts, you need to set your Discussion settings appropriately for your requirements
Your Discussion settings can be found within the Settings tool, in your blog’s dashboard:
These are the default settings for your blog (click on the image to open it in a new window):
To enable comments for every post in your blog, place a check in the “Allow people to post comments on articles” checkbox, scroll to the bottom of the page and click Save Changes. The WordPress Codex provides detailed help with what each setting is and what it does.