The copy/paste action from other text editors or internet should be done with "Ctrl + Shift + V" keyboard combination (or right-mouse-click and "Paste as plain text") so that all previous text formatting is removed.
Note: For Mac/iOS the "Paste as plain text" keyboard shortcut is "Cmd + Option + Shift + V" or sometimes "Cmd + Shift + V" depending on Mac browser you have.
After all previous text formatting is removed, the formatting needed can be added inside Body text with available format tools.
If you find any text inside the Body text field to be strangely formatted already - you can clear all formatting with the following steps.
After that you can add desired formatting with available editor tools.
Note: the "Cut" action is equal to Copy+Delete actions.