The tag library file (*.tld) are located in the META-INF directory and sub-directories of your struts distribution.
In your case, in : struts2-core-22.214.171.124.jar\META-INF\struts-tags.tld.
If you have a servlet/jsp container compatible JSP 1.2+; at container startup, all the library (*.jar) in WEB-INF/lib are scanned and the TLD files are located and loaded.
For each tld file it finds, the container looks for the <uri> element and saves a mapping between the uri and the current location of the tld.
After in your jsp, you have just put the directive for use the library.
In your case :
<%@ taglib uri="/struts-tags" prefix="myStrutsprefix" %>