Save the files pst-electricfield.sty|tex|pro in a directory, which is part of your 
local TeX tree. 
Then do not forget to run texhash to update this tree.
For more information  see the documentation of your LATEX distribution 
on installing packages into your LATEX distribution or the 
TeX Frequently Asked Questions:
(http://www.tex.ac.uk/cgi-bin/texfaq2html?label=instpackages).

The documentation -------------------
To get a smaller size of the generated pdf file run the
Makefile or by hand 
"pst2pdf <file> --Iext=.png --Iscale=0.5 --DPI=150". This will 
create eps/pdf/png images in a subdirectory images/ and then
using only the png ones for the last _pdflatex_ run. The
file size can be reduced to about 20% of the one created with 
ps2pdf. The pdf file is saved as yfile>-pdf.pdf.

When running the documentation in a traditional way, then
uncomment the line (in the preamble)

You can also use the Makefile.latex to create all three languages
of the document, or alternatively Makefile.pst2pdf to create them
with png imgaes to get smaller file sizes.