Question on adding space in the editor

Hi Folks:

I'm fairly new to using PHPStorm.

My problem:   When I try to type code into the editor, I can't add anything new  because it won't add any space.  That is If I have a string and try to add another word in the middle of the string it just overwrites what is already there. 

What setting am I missing in the editor that will allow me to add and edit things in the editor without overwriting what is there  (If I add something to the beginning of a line I end up having to re-write the whole line).

Example:

If I click to the left of "Counter... " and want to add a word, it just wants to overwrite the word Counter:     

echo "counter is $counter <br>";

I'm sure it's something simple.

Thanks for the help...

Matthew