How do you use a class from a .dll file?

I'm trying to use a class, "DevIO", from a Microchip library, "MCP2210-M-dotNet2.dll". When I downloaded the library, it had a managed and unmanaged folder, but Unity is reading both of them as native plugins. Supposedly, DllImport is used to access methods from a native plugin, but how do I access a class?