I haven't used vb.net. I've used VB6 to make a DLL, and guess it's
similar. So I will answer from that background. A DLL has one or more
Public objects of which a calling application can make an instance of.
The Public object will have properties and/or methods that can be
used.

For example, here are some lines of code from a project.
Public moCntrl As Calm.Cntrl
Set myCntrl = New Calm.Cntrl

Calm is a DLL. Cntrl is a Public class which has several Public
objects and methods.

To use the DLL In Excel, it will need a reference in the VB Editor
using the menu Tools | References.

Hth,
Merjet