qplot is intended to be similar to base r plot()
function, trying to always plot out your data without requiring too much specifications.
basic qplot
qplot(x = disp, y = mpg, data = mtcars)
adding colors
qplot(x = disp, y = mpg, colour = cyl,data = mtcars)
adding a smoother
qplot(x = disp, y = mpg, geom = c("point", "smooth"), data = mtcars)