This is a short plug for mathworksheetsgo.com free online graphing calculator which is a great tool for exploring graphs of various functions.
You start with this form.
Add one or more lines by clicking on buttons to the right
Click the Graph button at the bottom of form (not shown here)
And you get a graph like this.
This has only scratched the surface of what this tool can do.
Go here matworksheetsgo.com free online graphing calculator and have a play. If you have children them let them have a play too.
When I were a lad we had to do all this with graph paper and pencils!