All bonds are not created equal. Some bonds perfectly share their electrons, and others barely share them at all. A dipole moment is the mathematical expression that describes this disbalance.
General rules:
The sum of all dipole moments is equal to the net dipole. If all dipoles perfectly cancel out, the molecule with have no net dipole.
Concept #1: How to tell the difference between ionic, polar and covalent bonds.
Practice: Which molecule/s contain/s net dipoles?
Practice: Which molecule/s contain/s net dipoles?
Practice: Which molecule/s contain/s net dipoles?
Practice: Which of the solvents are apolar and polar?