Lemongrass is an aromatic grass, that has a delicate but pungent taste not unlike lemon. Its used in Thai cooking especially in coconut milk chicken. I use it in chicken and veggie stir-fries all the time. I know people who love eating the whole thing but usually you either just put the grass in the cooking and discard it or you pound it and get out the soft inside and use that. Either way it's great. Don't use too much at a time, it can be quite strong.
I used it with squash in Veggies on the Barbie