In 1984, what do these 3 slogans mean: War is Peace, Freedom is Slavery, and Ignorance is Strength?

At first glance, these slogans seem to be contradictory
and illogical.  And, they pretty much are, but the society in 1984
is run by a group of people that have pretty much brainwashed or intimidated
the entire population into believing whatever sort of nonsense they promote.  So, these
three slogans are lived by and sworn by, and the essence of everything that the Party
represents. Each of these three slogans have double meanings--one for the Party and one
for the people as a whole.

First of all, let's look as War
is Peace.  In their society, keeping the masses believing that constant war is being
waged is actually a way of maintaining peace.  War elicits great patriotism and devotion
to country; it also promotes sacrifice and giving to the community over oneself. So, if
there is constant war, the people are constantly giving, sacrificing, and pledging
devotion to their government.  This keeps the people in check and in control, and hence,
peaceful.  That is how the Party uses that slogan.  The people think it just means that
world peace is maintained through war.  Without war, their security would be
threatened.

Freedom is slavery is more tricky. The people
probably believe that to mean that having total freedom is actually a way to become
enslaved to your senses, weaknesses and vices.  For example, the Party encourages young
women to remain virtuous and restrict themselves from being romantically involved or
sentimental in any way.  The society has firm beliefs about sex and relationships--there
is very little freedom there, because they feel that sex and relationships enslave
people.  If you are constantly embroiled in relationships, you are subject to the
turmoil and unhappiness that they sometimes cause, and are constantly thinking about
it.  That is not freedom, according to them.  So, to the people and the masses, they
have been taught that freedom to act, and sometimes act poorly, actually tends to
enslave one to sentimental and unessential vices and emotions.  To the Party, a free
people represents the removal of their power.  So, the people must not be free in order
to remain in power.

To the masses, being ignorant about the
true condition of things is actually beneficial, because it helps them to remain happy
and optimistic, and thus strong.  To the workers within the Party, like Winston, their
entire jobs rely on keeping the people ignorant of true facts and statistics. 
Essentially, lie to keep the people in the dark, and then the Party--and their
jobs--will always be strong.  The people's ignorance gives the Party strength; if they
really knew the true state of things and how they had been manipulated, they would
rebel, and take away the Party's power.

In the end, it all
comes down to the Party creating slogans that ensure the continuation of their power and
control.  I hope that helps; good luck!