To create a blog post on your website first login to the website editor, if you don't know how to access it please see this article:
Once logged in, click on the "Blog" section:
From there click on "Add New Entry":
From there you can create your blog post, if you are trying to paste content into the text fields you will be unable to do so by using your mouse. To paste content into those fields you need to use your keyboard; on a PC use CTRL+V to paste, on a Mac use Command+V to paste.
Make sure to select the category and language at the bottom then click "Save Entry" and you're done!