colas are the main top bud sites that end up growing into each other making the look of one large bud. ever heard of a solid single cola plant? its cause they grew it short from clone and all the sites grew into each other. nodes are the intersections between leaf sites. for instance the first set of leaves is the first node, second set, the second node, etc. i wait until it has spit out 5 nodes before topping. you top by various methods, but i cut the small set of leaves that havent spread out yet (they look hed together sticking straight up. some cut below this to encourage lower growth to catch up with the top. when you cut, the node, or set of leaves below the cut take over as the main new growth and the plants energy is sent to the top where these two sets of leaves are. when you cut really depend on the health of the plant. my white widows spit out five finger leaves on the third set, so i can cut on the fourth. i always let it have 5 fingers first to reduce the stress from cutting and prevent it from hermie. if you are going to grow it out and tp it to 4 colas, id cut as soon as i could, then let it recover for a week, and cut again. if the plant gets cut when its already 2' or more you end up with a tall plant due to the exrta veg time for recovery. depending on how strong your light is will depend on the growth of the bud. for example i use 400w hps lights and they really dont promote much fruiting below a foot of the canopy (the top of the plants).