Suppose the dll name is SampleModule.dll and your module class name
is sampleClass then add a entry in web.config as below:
<add name="SampleModule" type="SampleNameSpace.SampleClass, SampleModuleDllName" />
Above config item you can add to web.config of an application
if you want only that application to use that.And you can put it in
machine.config if you want all the application on the server to use it.