Minecraft Mod Coding [PLEASE HELP]

Hello everyone, i have been working on a mod and i have got my art and code almost done. I just need help with figuring how to make somthing shoot out a block. I am making my own kind of staff mod (My 1st mod ever) and i have no idea how to make it so it can change blocks to snow or ice . So if someone could help me out and tell me what i add to my script/code that would be very appreciated!
Thank you very much , Ben
I want the item to shoot out ice blocks of some sort maybe ill create an ice cicle to use or somthing. Please help me i have no idea were to get such a code.!