Physics as a whole is indeed a very interesting subject and so is the case of Mechanics. However, one thing is clear, you have to understand the fundamental principles governing verging a certain law. You need to have a clarity in understanding the different approaches and then only you can arrive at the concluding result.
To make you understand the initial velocity at which a stone is thrown upward. It must reach a maximum height before it should move down ward. In that case, the final velocity of the stone is zero prior to its downward movement. Since at the initial stage the stone is moving upward and so applying the formula 0= U Squre - 2 g H since V = 0 when the stopped prior to coming downward. We can calculate the initial velocity U easily in terms of meter per sec where g is equal to 9.8 meter per sec.
So, in order to grasp the entire mechanism, you would require a sound tutor who can understand your problem and can guide you accordingly. Will it not only strengthen your fundamentals, it would arouse your interest further in learning different concept of Physics including Mechanics.