how is a lipid bilayer formed?

Answer 1

the phosphlipid bilayer consists of "water loving" =hydrophilic phosphate, and "water hating"=hydrophobic lipid. Phosphate and lipid are a single unit resembling a circle with two tails extended from it. Phosphate is the circle and lipid are the tails. Because of their reactivity with water, molecules arrange themselves in a double layer like so

0 0 0 0 0 0 0 0 0 0
/\ /\ /\ /\ /\ /\ /\ /\ /\ /\
\/ \/ \/ \/ \/ \/ \/ \/ \/ \/
0 0 0 0 0 0 0 0 0 0
each circle and two tails represents the phospholipid molecule. In arranging this way the lipid are protected from the water forming a barrier.

Answer 2

The phospholipids are "floating" on the outside of the cytoplasm of a cell. They make themselves into a bilayer because the phosphate heads are attracted to water and the lipid tails are repelled by water. The environment both inside and outside the cell contains water, so the heads turn toward the outside and toward the inside. The lipid tails are left in the middle of the bilayer, pointing toward each other and protected from the water.

See this animation for clarification:
http://trc.ucdavis.edu/biosci10v/bis10v/week2/fluidmosaic.mov