My teacher gave me a plan graph with the x and y-axis (like a right angle but upside down) she didn't label the axis's but it says I have to graph the equation that represents each situation. I am just confused by what she wanted me to graph on the graph?

I believe what your teacher wants is the x axis is the positive axis, the y is negative (since the submarine is going DOWN, y is negative (in feet), at 10 feet per second. The x axis is seconds, the y axis is feet. Graph the number of seconds on the x axis and then the y is in negative feet. At 0 feet, the submarine is on the surface, just like airplanes would have 0 feet on the ground. The difference is the submarine goes (if you like), negative feet below the surface, whereas planes go up (above) ground and have positive feet.