First of all take 3 values of x for example 1, 2 and 3.
Then do the calculations as follows:
y=3×1-6=-3
y=3×2-6=0
y=3×3-6=3
These values that we obtained you are gonna put in a table that's gonna look like this:
| x | 1 | 2 | 3 |
| y | -3 | 0 | 3 |
Then put the values in a chart, and build the graph.