Forward rolls take some considerable practice to achieve perfection. It can take years of practice. A forward roll is pretty much what it says. It is a three string, 3 note roll played on three string sets typically played in some chord structure. Forward rolls sound really good when they are played with a legato feel. They are somewhat arpeggios. Some great legend country guitarist like Chet Atkins, Merle Travis and numerous Jazz players often used forward rolls. They are not real common in popular music of today, but are still a good tool to have in your belt. They also work as a great conditioning tool to achieve finger coordination and strength.  


Look at this example using a C chord.


Another type of forward roll would be playing the same string sets and moving up the neck instead of across. These also sound really good when played with a legato feel. Check this example out in G.


Here is a tricky but awesome lick you may recognize. It is a somewhat a modern lick incorporating forward rolls.