How do i 'make' weapons

Can someone tell me how to 'make' weapons etc. because i have great ideas for a mod
King J wrote:the problemb is when i creat the projectiles for the guns ( i.e. Lockpick rocket {DONT COPY THAT}) the projectile wont come out the gun or whatever is firing it. However I can summon the Lockpick Projectile, it just wont come out the gun.