Well, the maths part of VB is pretty standard. Addition is like 1+2, multiplication 2*3, exponentiation 3^4. Invoke functions using their name Sin(6) or Sqrt(12), text is entered with double quotes "Hello Scripting". If you have a specific question someone can type up an example.
The major difference between Expressions and VBscript is that expression only allow you to enter a single statement. So no variable declaration or ifs or loops. It’s really very limited, but that often suffices.