Lettuce

Meat-eaters look away, this is a vegetable blip! This is my very own lettuce that I have been growing since February 28th. The lettuce and the arugula survived the move outside, the peppers and the tomatoes did not. Can anyone tell me how/when we can begin to eat these? If I cut off lettuce leaves do they grow more? Or is that plant done? Is there some way to go about it? All advice appreciated.