The correct location to place your new style.css

1. On the server folders, open httpdocs > wp-content > themes
2. Then in your theme's folder create a folder specially for your child's theme - something like twentyfourteen-child.
   
   Right-click to Create Directory.
   
   
   New directory now created.
   
   
3. Create your new style.css file - I've use SublimeText below.
   [ To see this view in SublimeText make sure you select View > Syntax > CSS ]
   
   
   Enter this important code and add in your details, then save the file:
   N.B. You must enter the right code to make this work.
   /* Theme Name: Twenty Eleven Child Theme
   Theme URI: http://YOUR_SITE_URL/PATH/CHILD THEME NAME
   Author: YOUR NAME
   Author URI: http://YOUR_SITE_URL
   Description: The new child theme of Twenty Eleven created by me.
   Template: twentyfourteen
   Version: 1.7
   */
   
   @import url('../twentyfourteen/style.css');
   
   /* Theme customisation starts here
   ----------------------------------------------------- */
4. Upload your style.css file into newly created folder.

The other names of Theme Name, Description and Author are completely up to you.

The Template identifies the parent theme, while the @import imports the CSS from that original theme. The path to your parent theme’s .css file must be correct so that the 'Template' parameter can correctly identify the name of your parent theme. If you want to use a different theme, then just change these values accordingly.

NB. Everything is case sensitive! The folder of our parent theme is 'twentyfourteen' all lowercase, and the @import URL reflects this.

Now, you are almost ready to go, but you must Activate your new theme...

SEE HOW TO ACTIVATE THEME HERE