You can add a Read More break to your post in the content editor to show where this summary should end.
It enables you to specify where the summary break happens and provide a flavour of what the post is about. So, your readers can scan headlines and summaries more quickly, and want to see more!
How to use read more break in your posts?
Click More Misc in your content editor.
In the popped-up toolbar, you will see Read More Break.
Place your cursor where the summary break happens and click Read More Break, and that's all!
And let's see how it is seen in your sidebar;