help with 2nd HDD...

i have two HDD's in my computer, a smaller one to have as a sytem drive and a larger one to put all my files on. It reconizes the 2nd drive but when i click to open it i get an error say it can't mount becuase the drive isn't listed in /etc/fstab. i tried adding the drive to the list with the location /files and now it just says that the location / files doesn't exist. what do i need to do so i can get my drive properly mounted and read-write capable.