gnuplot: `with` plotting style dictates `using`

gnuplot plotting styles are specified by the with keyword to the plot command:

help with
plot 'foo.csv' with <style>

Each plotting style has different requirements on the fields of each row to plot. By default, as many fields as needed for that plot style will be looked for on each line in order but the using statement lets you explicitly select the fields to use.

To plot points or lines there must be two fields; x, y:

plot 'foo.csv` with points
plot 'foo.csv` using 1:2 with points
plot 'foo.csv` using 3:2 with points

To plot labels three fields are needed; x, y, label:

plot `foo.csv` with labels
plot `foo.csv` using 1:2:3 with labels
plot `foo.csv` using 3:2:5 with labels