[header] How to start a relationship with a girl who's just told you she likes you [title] Be casual. [step] Don't go jumping around in front of her yelling out " yes! ! She likes me! Yeah! ". This isn't a good idea, it doesn't rate very high on the coolness scale. 
No matter what you're feeling inside, don't let it show too much. Obviously, you don't have to be stony-faced and speak in a monotone voice, but just don't get really worked up.