A straight line is usually written as $y=mx+c$. In this form, $m$ is the gradient and $c$ is the y-intercept.

The y-intercept is where the line crosses the y-axis, so it happens when $x=0$. A positive gradient rises from left to right, a negative gradient falls, and a horizontal line has gradient 0.

The crossing point is $(0,c)$. This means you can read a lot from the equation before you even draw the line.