Hello there,
I am an extreme amateur, 1st time builder. I am making a shooter robot and grabber.
My grabbing module is ready ...... But I am not able to make a shooting module.
Any ideas ? 
Thank-you for your concern
Mohit Gupta 
What do you want the "shooting module" to do?
Shoot at targets which will be detected by ultrasound sensors
I am making one from scrap but with no success till now
What have you gotten to work so far? Are you able to locate targets with ultrasonic sensors? What are you shooting at the targets?
Yes it finds targets and I am planning to shoot marbles or nerf bullets....or any other you can suggest
Marbles are probably dangerous to shoot. They are hard and can easily break things or cause major injury. Nerf darts are fine if you only want to shoot one or two. If you want repeated shots you could use a semi-auto paintball gun which would only require a trigger pull to shoot. If you could find soft projectiles (like Nerf balls) the size of paintballs that would make an excellent choice. Something like these:
http://www.goldduo.com/paintball-c-1650/blem-reusable-dense-foam-paintballs-400-balls-p-649589