If you are doing so you've already written some COM compatible classes.

The next steps are to:
1. Use sn.exe to create a key and give your assembly a strong name.
2. Use tlbexp.exe to generate a type library.
3. Use regasm.exe to register the assembly and use the /tlb switch to
include the type library.

If you want to do this manually there a numerous articles. Search for
"expose .NET to COM".