Do you have a long post content and feels like it is better to split then into two page, its just two simple step:

Step 1:

In HTML mode add the text <!–nextpage–> where you want to break the page.

Step 2:
If Step 1 does not work for you then you need to check your single.php in your theme folder and locate if wp_link_pages() is there and if not add it.

Let me know if you are not able to make it work, shall help you fix it.