On a graph, the x-axis is horizontal and the y-axis is vertical. The axes cross at the origin, and a point is written as $(x,y)$ so you always read the x-coordinate first and the y-coordinate second.

Each straight-line graph shows all the points that satisfy one equation. When two lines cross, that point satisfies both equations at the same time.

That is why the intersection gives the solution to simultaneous equations. If the crossing point is $(2,3)$, you write the answer as $x=2$ and $y=3$.