The given linear equation is:
$$ \color{blue}{ 3x+y = -3 } $$To find y - intercept we substitute $ \color{blue}{x = 0} $ into line equation.
$$\begin{aligned} 3x+y &= -3 \\ 3\cdot \color{blue}{ 0 }+y &= -3\\y &= -3\\y &= -3 \end{aligned} $$So, the point $\left(0, -3 \right)$ is on the y axis.
To find x - intercept we substitute $\color{blue}{ y = 0 }$.
$$ \begin{aligned} 3x+y &= -3 \\3x+\color{blue}{ 0 } &= -3\\3x &= -3\\ x &= -1 \end{aligned} $$So, the point $ \left( -1 ,0 \right) $ is on the x axis.
The graph of the function is: