OK,
the concept is to add the shrimp into the tank....the shrimp begin to decay (rot) giving off ammonia which spawns the ammonia eating bacteria into action. this creates a microorganism bloom, as these bacteria absorb the ammonia they give off nitrite - which then spawn a microorganism bloom of nitrite eating bacteria. this is why you have an ammonia spike followed by a nitrite spike.
You can remove the shrimp when your ammonia spikes. Your nitrites should spike and when the nitrites reach nearly zero this is the time when you can add some hardy fish (I prefer clowns) and your tank is on it's way.