A linear equation is something that produces a line on a graph found in the format y = mx + b with m as the slope, b as the y-intercept (when x = 0), and x & y as the points on the graph.
A simple linear equation is y = x. Note, that this is basically a line passing through the origin (0,0) and is diagonal. Since y =x, we get a line with a slope of 1.