This equation is in slope intercept form y=mx+b
In this form
y=the value for y at a given point
x=the value for x at a given point
m=the slope of the line
b=the y intercept of the line
You know that your y intercept is 6 because your b value is 6. Your first point should go at (0,6)
You also know that your slope is -1 because -1 times x is -x
We can take -1/1 and we get rise over run for our slope
from (0,6) we go down 1 and 1 to the right to get (1,5) down 1 and 1 to the right again to get (2,4)
You now have 3 points, draw a line through those points and you get something that looks like this.