2 - Divide & Conquer
The easiest way to tackle a large problem (or project) is to split the larger problem into smaller problems and tackle the smaller problems, combining them into a final product. Consider baking - the final outcome is lovely but it is a complicated product made of smaller "problems", each tackled by the chef and sous chefs one-by-one.
In computer science, it is no different. If we can reduce a larger problem into the sum of smaller problems, we can write algorithms that are more efficient at completing certain tasks.