You must have seen long wordpress posts spanning multiple pages.The bottom of the posts will contain the page numbers.Numbering the page breaks contained in your posts is the feature of your theme and almost all modern themes have this feature,However you will have to insert the page break manually inside your wordpress post at the place you would like the new page to appear.It is also a good idea to write a brief introduction of the contents of the new page towards the end of the previous page.
Here is a example of a post with multiple pages on this website.
Post with multiple pages example
To split the post into multiple pages you will nees to insert a page break into your post at the appropriate place.
Go to your post in text view and insert the following code
<!--nextpage-->
Now when you go to the visual post editor you will be able to see a PAGE BREAK inserted and when you will open the post you will be able to see the posts pages numbered provided your theme supports this feature.
That is all.
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