There are three ways to go about this:

Set date prefix to a future date

Simply set your blog post date prefix to a future date to prevent the page from being rendered during site generation.

Save post as draft

Drafts are posts without a date in the filename. They’re posts you’re still working on and don’t want to publish yet. To get up and running with drafts, create a _drafts folder in your site’s root and create your first draft:

|-- _drafts/
|   |-- a-draft-post.md

To preview your site with drafts, run jekyll serve or jekyll build with the --drafts switch. Each will be assigned the value modification time of the draft file for its date, and thus you will see currently edited drafts as the latest posts.

Mark post as unpublished

Add published: false in the YAML front matter if you don’t want a specific post to show up when the site is generated. published is a predefined global variable in Jekyll. To preview unpublished pages, run jekyll serve or jekyll build with the --unpublished switch.