When copying text from other programmes or websites, it is important to paste the content as plain text and to strip off complicated formatting first. Otherwise, you run the risk of copying in special formatting or hidden code that can interfere with the source code of your website.
There are different ways to do this but the simplest is to use the below keyboard shortcuts for pasting the text.
Windows: Ctrl + Shift + V
Mac: Cmd + Option + Shift + V
Another option to strip off formatting is to paste the text into a simple Text Editor, that strips out complicated formatting and then copy and paste the text from there into your web pages.
Most devices have simple Text Editors installed. On Windows, you can look for Notepad and on Mac for TextEdit.