Scatter graphs tell you how closely two things are related….which is called “correlation”.
If you can draw a line of best fit on your graph quite close to most of the points then you have strong correlation. If not you have weak correlation.
If the scatter graph slopes up from left to right then you have positive correlation, i.e. both things on the graph increase together.
If the scatter graph slopes down from left to right then you have negative correlation, i.e. when one thing on the graph increases the other decreases.
Here’s a handy guide:
If you get a scatter graph in the exam you might be asked to draw a line of best fit. Just take your ruler and draw a line that goes as close to all the points as possible. You can then use this to estimate values you don’t have data for.