Those instructions assume that you are building a JSP-based webapp that is using content from an Alfresco repository, and that you want to make use of the Web Editor functionality to edit that content.
In this scenario, the WEB-INF/lib folder mentioned is that of your webapp. For this particular set-up, you should have at least three webapps in your Tomcat instance: alfresco.war, awe.war, and your own webapp (with the Web Editor taglib installed in it).