y+x=-3
y is represented by a vertical axis and x by a horizontal axis.
If you are using graph paper, draw a line roughly down the centre of the page from the middle of the top to the middle of the bottom. Use the divisions and subdivisions of the graph paper grid to draw the line along the thicker divisions (major divisions). That's the y-axis. Draw a line from the middle of the left edge of the paper to the right edge. Again, use the graph grid as a guide. That's the x-axis.
The graph of x+y=-3 is a straight line. If we put y=0 in this equation, then x=-3 (x-intercept). Mark -3 (3 major divisions to the left of where the axes cross (the origin where x=0 and y=0, the point (0,0)).
If we put x=0, then y=-3. Mark -3 major divisions below the origin. Draw a line as long as possible which passes through the two marked points on the axes. That sloping line is the graph of x+y=-3.