You start by drawing vertical lines from each of the corners of the graph - where you have drawn dots/plotted points.
In the first case this divides the whole thing into a series of triangles and rectangles, which are easy to find the area of.
In Part 1 Sections A,B & C are above the time axis, so represent positive areas for displacement.
Sections D, E & F are below the axis, so represent negative areas for displacement.
Lets pretend the areas under A,B&C was 200, and the Areas fro section D,E&F was -300
That would represent a total displacement of -300, but a distance covered of 500
Since the time was 720 seconds, that would mean average velocity = -100/720 while the average speed would be 500/720
Similar working for part 2 except you have to estimate some areas as the bounding line in some cases is a curve.
If you know the equation of the curve, you could use integration but in physics we usually use either a "counting the squares" technique, or approximate to triangles/rectangles.