war ant task documentation in Ant manual:

http://ant.apache.org/manual/CoreTasks/war.html

An example I did some time ago:

<target name="dist" depends="compile ,javadoc">
 <war file="${dist.home}/${app.name}.war"
webxml="${web.home}/WEB-INF/web.xml">
   <fileset dir="${build.home}">
     <exclude name="**/web.xml" />
     <exclude name="**/*.java" />
     <exclude name="**/*.class" />
   </fileset>
   <lib dir="${basedir}/lib"/>
   <classes dir="${build.home}/WEB-INF/classes">
     <exclude name="**/*.java"/>
   </classes>
 </war>
</target>

Note the proper filesets will depend on your environment.

Tomcat tasks examples:

<taskdef name="deploy"   classname="org.apache.catalina.ant.DeployTask"/>
<taskdef name="undeploy" classname="org.apache.catalina.ant.UndeployTask"/>

<target name="install" depends="dist">
    <deploy url="${manager.url}"
       username="${manager.username}"
       password="${manager.password}"
           path="${app.path}"
            war="${dist.home}/action.war"/>
   </target>

<target name="remove">
    <undeploy url="${manager.url}"
         username="${manager.username}"
         password="${manager.password}"
             path="${app.path}"/>
</target>

-All is configured with a build.properties which assigns ${xxx}.
-You must include catalina-ant.jar (in Tomcat's server/lib folder) in your
classpath
-To remove an application, it's better to stop it before, with the stop task
(there are also start, list,...)
-Tomcat docs (not much) about its Ant tasks:
http://tomcat.apache.org/tomcat-5.5-doc/manager-howto.html#Executing%20Manager%2
0Commands%20With%20Ant
-Sometimes one or more webapp jars get locked and the remove undeploy task
doesn't work properly if you don't restart Tomcat. In that case, change
Tomcat's context.xml to <context antiJARLocking="true"> ... </context> to
prevent this to happen (only in development, as it will slow down things a
bit)

ant comes with docs.

My experience is that the documentation of tasks is sufficient
to use them.

Arne