To complete the table, substitute the x-value into the equation and solve for the y-value.

The general equation of a straight line is 

     y = mx + b

Where " m " is the slope of the line. 
And   " b " is the +/- y-intercept of the line.
The y-intercept is the point on the graph where the line crosses the y-axis.
Similarly, the x-intercept is the point on the graph where the line crosses the x-axis.

Now,   m = vertical rise of the line/horizontal run of the line.
If,  m is positive (+), then the line direction is SW-to-NE (/) and
if,  m is negative (-), then the line direction is NW-to-SE (\).

To find the y-intercept of a line, let x=0 and solve for y.
To find the x-intercept of a line, let y=0 and solve for x.

A line parallel to the y-axis has an equation of the form, x = number.
For example, the line x=2, is two units to the right and parallel to the y-axis.
Likewise, A line parallel to the x-axis has an equation of the form, y = number.  
For example, the line y=3, is three units above and parallel to the x-axis.