How to remove Spam pages from wordpress [Non related page got indexed]

Recently i have seen on my website that there are tons of pages indexed even i have not created and they are not in my wp dashboard its just a spam don't know how these pages get indexed on my domain..
I have just checked site:thegamehelp.com
There are spam pages like this – thegamehelp.com/gjtcqtwh-3511.html i haven't created this one and could not find this on dashboard.. someone please help.. how to prevent them too..

See original post by Rinki12