There is a tip specifically for this, actually! If you are using buttercream or royal, you can use tip #233. Or, you could also use fondant and cut little strips, depending on which look you're going for. Good luck, and welcome to cake central! You'll be addicted in no time... 
HTH
Diana
I'm new to this and want to make "grass" for a golf themed cake. Can you help?
Get tip #233..its especially made for grass...it has multiple openings on the top. You squeeze close to the surface of the cake and lightly pull up and release..and TADA you will have grass
Woohooo...I can do that. Thanks. What a great site...a definite addiction! Who knew?!
Welcome to CC...the addiction here is overwhelmingly awesome..glad you got the answers you were looking for.
Happy Baking, Mary 
the tip 233 works great. Looks like a thimble on top. Just make sure your icing isn't too stiff and squeeze a good bottom to attach it to the cake before you pull up- I learned that one the hard way! This tip also makes great hair on people or animals. For a more chunky or cartoony look you can also pull out tip #16 strands.
Have fun!
Quote by @%username% on %date%
%body%