Sage can plot using matplotlib, openmath, gnuplot, or surf but only matplotlib and openmath are included with Sage in the standard distribution. For surf examples, see 3.6.
Plotting in Sage can be done in many different ways. You can plot
a function (in 2 or 3 dimensions) or a set of points (in 2-D only)
via gnuplot, you can plot a solution to a differential equation via Maxima
(which in turn calls gnuplot or openmath), or you can
use Singular's interface with the plotting package surf
(which does not come with Sage). gnuplot
does not have an implicit plotting command, so if you want to
plot a curve or surface using an implicit plot, it is best
to use the Singular's interface to surf, as described in
chapter 15, Algebraic geometry.