What is the difference between the use of B and V? 

Use of the B

After M there is always a B, example: shadow, samba, change, combine.

Use of V

Applies after b,d,v. Example: guess, come, send, adverb.

Other examples of the application of B and V

• He was going home when they called him.
• VAT: value added tax.
• The cell phone would have cost me cheaper if it hadn’t been for VAT.
• Hiba: It doesn’t exist.