This page is relevant when, and only when, building shared assemblies. To build a shared assembly you need a digital certificate to sign the assembly. See Building Shared Assemblies for more information. The assembly signing certificate is used to sign the shared assembly and the file signing certificate is used to sign the MSI file created for this assembly.
The above dialog has both certificate fields empty - no certificates are selected. In this case Manifest Maker will use default certificates selected in the Build Options dialog. If certificates are selected or the current selection is invalid, the build will fail.
To select a certificate click the Choose... button. Select appropriate certificate from the displayed list and click OK. Manifest Maker will extract identification information from the selected certificate and fill in the correspondig fields:
Numbers in this image are an example, they are of no use to you - yours will be extracted from your certificate.