Difference between histogram and frequency polygon?

They are the same thing except that in a histogram you are using bars (like in a bar chart) to show the frequency, while a polygon uses points connected by straight lines

The way I have the students do it is to plot the x,y coordinates for your data ( x is the value of the random variable, y is the frequency )

If you are doing a frequency polygon, you just connect the dots with straight lines (you need to start at zero to the left of your first point and to the right of your last point)

If you are doing a histogram, just draw bars where the middle of each bar comes up to the x,y point