If you want to add your own custom pages or custom actions in SharePoint Central Administration, you need to create a feature for implementation. The below is the same piece of feature code that has a key attribute AutoActivateInCentralAdmin and it has to be true to make sure that your feature is visible on Central Admin.
<?xml version="1.0" encoding="utf-8" ?>
<Feature Id="91003Dd6-D88E-42ed-BF97-5C4C22BFA3CF"
Title="My custom Feature"
Description="Active By Default."
Version="1.0.0.0"
Scope="WebApplication"
Hidden="false"
xmlns="http://schemas.microsoft.com/sharepoint/"
ActivateOnDefault="true"
AutoActivateInCentralAdmin="true"
AlwaysForceInstall="true">
</Feature>
The AutoActivateInCentralAdmin works with all other scopes, but only activates the feature on the CentralAdmin (WebApp, Site or RootWeb)