Whats the difference between a genotype and phenotype?

A genotype is an organism's
genetic makeup. In other words, what genes it has for a particular trait. For example,
if you are referring the trait of height in a pea
plant,  there are two different genotypes that can produce a tall pea plant. One
genotype is TT ( the capital T stands for the tall gene or allele) therefore, two
capital T's could produce a pure or homozygous tall pea plant. Another genotype for
tall, is Tt (the capital T refers to a tall gene and the lower case t, a short gene).
Although the plant has one of each type of gene for height, because the tall gene is
dominant over the short gene, this will still produce a tall offspring. That is because
the dominant gene (T)will be expressed and the recessive gene(t) will be hidden in this
case. A third genotype exists for height in pea plants and that is two lower case t's,
or tt. This genotype will produce a short pea plant.  To summarize,
genotype is the pair of genes an organism has for a particular trait. 

Phenotype is the observable
trait present in the organism. For example, if you were to see the pea
plants in a garden, the TT and Tt will both appear tall.  And, if you saw the tt plant,
it would appear short. So, basically  if a plant is TT or Tt, you will see both as tall
plants and would have no way of knowing what genetic makeup each one had, through simple
observation. 

Another example can be handedness in humans.
There is the trait of right-handedness and left-handedness. The gene for right
handedness is dominant over left handedness. Therefore, three genotypes exist- RR, RL,
LL.  The person with a genotype of two R genes is a righty.  The person with a genotype
with a righty and a lefty gene, RL is also a righty. That is because the right handed
gene is dominant. The last genotype, LL is a lefty. The only way to produce the
recessive left-handed person is two have to L genes. Therefore, there are
three genotypes for handedness in
people.

However, there are
only two phenotypes:  A person is either a Righty or
lefty.   

Question: Which person's genotype
is always the same as their phenotype?

Answer: A
lefty- if someone is a lefty(which is their phenotype), you always know their genotype
must be LL!