Auto down the line when using paragraph block

You have written a text without any spaces. As your theme has not provided for this, the browser standards apply and everything is displayed on one line.

To solve this, you could add the following customised CSS:

.entry-content p {
 word-wrap: break-word;
}

You would have to insert this under Appeareance > Editor > Style > Additional CSS.

I also see that you seem to have entered something in the HTML code yourself. A class “123456” is set at the paragraph. This is not allowed. Class names must begin with letters.

Thank you so much @threadi , The problem solved