Answer
The y-intercept is $0$.
The slope is $-1$.
See the graph below.
Work Step by Step
First, we have to get the equation's slope-intercept form, that is $y=mx+b$.
Subtract $x$ from both sides of the equation to obtain:
\begin{align*}
x+y-x&=0-x\\
y&=-x\end{align*}
This form of the equation is the slope-intercept form.
In this form, the slope of the line equals to the coefficient of $x$ (which is $m$) and the $y$-intercept equals to the constant $b$.
Therefore in the equation $y=-x$:
The $y$-intercept is $0$.
The slope is $-1$.
In order to graph the line, we have to sketch the $y$-intercept, that is $(0, 0)$.
As the slope is $-1$, we can find another point that we can also sketch.
The slope is the change in $y$ for every $1$ unit change of $x$.
Thus, a slope of $-1$ means a $1$-unit increase in $x$ will result to a $-1$-unit increase (or $1$-unit decrease) in $y$.
Using $(0, 0)$ as the starting point and a slope of $-1$, the coordinates of another point on the line would be:
$(0+1, 0-1)=(1, -1)$
Plot the two points then connect them using a straigiht line.
Refer to the graph above,
