Could you please assist me, Part 1 In two dimensional motion, we treat the two motions as if they were separate, but in reality they are tied

Could you please assist me, Part 1

In two dimensional motion, we treat the two motions as if they were separate, but in reality they are tied together. What are some ways they are connected and how can this come into play in real world applications and situations?

Part 2

Newton's Second law of Motion (F = ma) is one of the basis of forces and motion. How is it very similar to his First law and why is finding the acceleration of the system (the main reason we use it) so important to solving physics and real world problems?