Although JCE is called the Most Popular and I would say the best editor for Joomla Sites.
But most of the times… on the very first install people are having problem with using the Editor… the Reason is sometimes it is automatically loading some CSS and aligning the text to center or giving a background or auto formatting the text.

The solution is simple.
1.  Navigate to components >> JCE Administration >> Configuration.

2. Now go down to the formatting tab and  make  use template CSS : NO

Save it and You are done!