Follow these steps to insert image:

• Click Tree icon (it is a 6th icon from the right in 2nd row of text editor).
• It will open a new window, if you know the url of image then paste it in Image URL field and click on insert.
  
• If image is on your computer then click on Browse icon.
  
• Again it will open a new window
• On the top of new window, there is a upload link. Click on it to Browse(choose) your local file and clik on upload
  and at last click on 'insert button' to add image in editor.