The + should just be taken to mean "add this layer to your plot". It's building up a graph object, whose print() method happens to also be its plot() method.

Basic graphics are actually tremendously powerful and can basically give you pixel level control. However the documentation is trash and many of the higher-level functions have hideous defaults.

Ggplot is great for fast iteration and exploratory data analysis, especially when "coloring by group" and "faceting" are involved.