How to start lucid dream?

iv been having nightmares for almost 3 er 4 years and i heard something about lucid dream? im not sure on what it is but i would looooooove to change my dreams. i have had dreams where i relize im dreaming and then just do whatever i want with no regrets but i dont think i have ever changed the scene or anything about it. how do i start a lucid dream? or how can i tell my sleeping body that i am dream. i do REM sleep pretty oddly. my mom will tell me that my eyes are moving verrrrryyy fast and that i move alot in my sleep (raise my arms move my legs, hands, and even make emotions with my face). sometimes ill laugh in my sleep and wake up and im laughing. or ill have and extremely disturbed face and my sister will wake me up and ask whats wrong. ill say things like yes or no or answer someone in my dream but answer aloud and people around my sleeping body will hear me >.< also i wake up and there are scratches on my face and i never know how they got there...so i move alot and talk but how do i start lucid dream? i dont know anything about it. will it help my every night nightmares? anyone know what to do?