hes just clarifying to you that when a plant grows in height and is very "stringy" it means that the plant is not getting enough light. so give it more light or maybe move your light bulbs closer to the plant.
however, when your plant is getting enough light it wont have any unnecessary stretching and thats what you should be aiming for.
you should also be aware of the different light spectrums. some bulbs produce a "white light" and others produce a more "yellowish" light. if you want to veg, focus on getting some white light bulbs and if youre flowering, use the yellow ones.
thats as basic as i can break it down for you. good luck and dont be discouraged. everyone was once a noob. cheers
Also each plant needs at least 3,000 lumens to prosper, plants like a light in the blue range such as Daylight florescent and mercury vapor in veg, and a light with pink/orange for flowering which is soft white fluorescent and high pressure sodium in flowering.