What are polar molecules and non-polar molecules?What is a polar head and non-polar tail?Is the structure of a cell membrane similar to that of soap?

In some molecules the atoms are arranged in such a way that one end of molecule has partial positive charge and the other end has partial  negative charge, such molecules are called polar molecules, while the other having no such electric charge are called non polar molecules. In non polar molecules the sharing of electron is equal between two atoms in a molecule, imparting no charge to such molecules.
 
Several classes of  molecules are such that they are having polar head that is hydrophilic i.e. inertacing favourably with water and a non polar tail that escaping from water.
Phospholipids are example of such molecules, which constitute an important lipid part of a cell membrane. Lipids are arranged as a bilayer. In membrane they are arranged with their hydrophilic  polar heads towards outer sides and hydrophobic tail towards inner side
These lipid molecule that constitute the cell membrane are similar to the soap bubbles. Soap bubble is also made up of lipid molecule that has a hydrophilic head and a long hydrophobic tail.