You get sample comments and posts in a fresh WordPress install. You can easily remove them in the following way.
Steps to remove Sample Comments and Posts From WordPress
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Log in to the WordPress dashboard.
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From the Dashboard menu, go to Posts and click on All Posts.

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Hover the mouse on the sample post and click on Trash.

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Now, do the same with the sample pages. Head to the Dashboard menu, hover your mouse on Posts, and click All Posts. Remove the sample pages.

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Similarly, you can remove sample comments. Choose Comments from the dashboard, hover your mouse over a comment and choose Trash.

After you take these steps, your blog will be clean from sample comments and posts.