The rest of Chap 4 will be seen later in the course and it is NOT covered in midterm 1.
An object moving in two dimensions will make a trajectory in the x-y plane. The instantaneous velocity is tangent to the trajectory and will generally have x and y component.
2D motion is basically 1D motion twice and all the relations we have seen still hold.
For the next question you need to use the definition of average acceleration
Motion diagram in 2D works the same way as in 1D. The velocity vectors connect two points in each motion diagram while the acceleration vector is shown on top the of the dot and come from the vector subtraction of the velocity after - velocity before the point.
The length and direction of the acceleration vector is hard to guess at first. Only careful subtraction of the velocity vectors will yield the answers.
Here is an example of 2D motion diagram with all acceleration vectors. The explicit vector subtraction is shown for point 4. Make sure you understand how the other acceleration vectors were obtained.