You've seen how to track "level + resource used" in Red Green Towers. Now I'll show you a completely different 2D (two-dimensional) pattern: moving through a grid. You're given an × grid. Some cells are empty (.), some are walls (#).
You start at the top-left corner (1,1) and want to reach the bottom-right corner (,). You can only move right or down. How many paths exist from start to finish? Before reading on, think: what two pieces of information do you need to describe where you are?