The slope of a line on a graph is the same as the slope of a hill or
ramp. The conventional way of measuring slope is to determine the ratio
of the rise, y-axis, of the line to the run, x-axis, of the line. A hill
might rise 10 feet for every 5 feet it runs, fairly steep ~63 degrees.
While an everyday ramp may only rise half a meter as it runs 2 meters,
~14 degrees. On a graph the rise and run have specific units. In our example
of heating a balloon the rise has units of volume (mL) while the run has
units of temperature oC. The slope would have the units of mL/oC.
Based on the slope we should be able to predict the change in volume of
a balloon for every oC it is heated or cooled. To do this use
the formula for the slope of a line:
You take the values you need from the line on the graph, not specific data points or the data table, unless the data truly lies along a straight line. From our graph pick two points where the line intersects with x and y gridlines, this makes determining exact values much easier.
That's pretty much it for graphing basics. Keep plotting along.