Unzip the distributed ZIP to any directory. You will get a directory named "jsunit".
You can also put the jsunit directory on a webserver. Then you can access JsUnit over HTTP. This method is particularly suitable when you have many people running shared JsUnit tests across an enterprise.
If you are going to use the JsUnit Server, jsunit/java/bin/jsunit.jar needs to exist. The distribution comes with a default jsunit.jar. If you have trouble with this JAR, you can easily build it for your machine using the jsunit/build.xml Ant file. The default target in this file is create_distribution, which builds the JAR. So can just execute "ant" in the jsunit directory to build the JAR.