Assembly instructions is the language that your processor speaks (Or rather machine code). Your processor does not directly execute VB, C, C++, or any other language.
An assembly instruction more or less directly maps to machine code.

VB.NET compiles to an intermediary language called CIL (formerly MSIL).
When you run your .NET application, the Just-In-Time (JIT) compiler will translate the CIL code to native code to be executed by the processor.
I'm probably missing some details in there somewhere but thats roughly how it works. Thats the relationship between VB and assembly instructions.