happy cheese,
y=2x+18 is the equation of straight line.
You know that x-axis is horizontal right.
Now, tilt a line that is along x-axis by 63.4 degrees (in the counter-clockwise) and push it up 18 units, then you end up with the line y=2x+18.
In the equation, '2' is called the slope. Sounds boring? Here 2=tan(theta) and theta=atan(2)=63.4 degrees as mentioned previously.
Is this what you needed help with?
Cheers,
Sai.
Note: The equation of x-axis is y=0. Does that make sense? Can you explain why?