SharePoint 2013: Adding a Blog to an Existing Site (without creating a new blog site)

use the below PowerShell cmdlets

Enable-SPFeature -identity "BlogContent" -url  "Sitecollection URL"

After enabling the feature go to “Site contents“ then you will find 3 lists named “Posts”,”Comments” and “Categories”.

Then u just navigate ‘Posts’ list and click an item then u will get the blogs UI