Step 1: Place any block of choice with a redstone torch on the front.
Step 3: Place 1 Redstone Repeater in front of the far left Redstone dust, and place 1 redstone dust behind it, and one on the block of choice.
Step 4: The redstone circuit should be flicking on and off. Place a dispenser 1 block away from the far right redstone dust in front of the block of choice.
Step 5: Fill the dispenser up with any throwable projectile. (E.g. Eggs, Fire Charges, Snowballs) Then connect it the circuit and dispenser with redstone dust and the dispenser should immediately start shooting out the projectiles.
An official redstone tutorial by hardpotatoes2.