Before you can start using SchemaSpy you must have installed two things in your system environment.
Download instructions for all operating systems: https://java.com/en/download/manual.jsp
The easiest way to install Graphviz is to download the msi package from http://www.graphviz.org/download/
Remember to add the folder containing Graphviz's dot.exe application to your system PATH variable, eg.
C:\Program Files (x86)\Graphviz2.38\bin
- Linux, Mac OS
Please read carefully the detailed instructions on how to install Graphviz on your os version http://www.graphviz.org/download/.
SchemaSpy is just a single executable jar-file (schemaspy-[version].jar), you can download releases from http://schemaspy.org or the github releases page https://github.com/schemaspy/schemaspy/releases
If you feel adventurous there is a link in the README.md for latest builds.
When you have your jar-file head on over to Get Started