The linear function $y=mx+b$ actually represents a graph of a straight line that has a point of intersection with the vertical $Y$ axis.

$m$ represents the slope.

When $m$ is positive, the slope is positive: the line goes upwards.

When $m$ is negative, the slope is negative: the line goes downwards.

When $m = 0$, the slope is zero: the line is parallel to the $X$ axis.

$b$ represents the point where the line intersects the $Y$ axis.

If $b=0$, then the line will pass through the origin of the coordinates, that is, the point $\left(0,0\right)$