WLST - how to install it

I tried to run WLST and got the following error:
C:\oracle\admin\mydomain\aserver\mydomain>java weblogic.WLST
Exception in thread "Main Thread" java.lang.NoClassDefFoundError: weblogic/WLST
Caused by: java.lang.ClassNotFoundException: weblogic.WLST
        at java.net.URLClassLoader$1.run(URLClassLoader.java:202)
        at java.net.URLClassLoader.findClass(URLClassLoader.java:190)
        at java.lang.ClassLoader.loadClass(ClassLoader.java:306)
        at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:308)
        at java.lang.ClassLoader.loadClass(ClassLoader.java:247)
Could not find the main class: weblogic.WLST.  Program will exit.

How can I install WLST on my machine?  It is a Windows server.
Thank you in advance!