What does c represent

The formula of a straight line is $y=mx+c$

$c$ is the point where the straight line crosses the $y$ axis ( $y$ intercept).

Do we need to remember this?

No because it is so easy to work out

C is represented as the Y axis interception

As follows:

$y=3x+1$ is the formula of a straight line

If $x$ is zero then:

$y=3times0+1$

$y=1$

The point where the slope hits the $y$ axis is:

$x=0$ and $y=1$

Likewise

The point where the line hits the $x$ axis is

$y=3x+1$

If $y$ is zero then:

$0=3x+1$

$3x=-1$

$x=-1/3$

The point where the line hits the $x$ axis is:

$x=-1/3$ and $y=0$