How does Candide satirizes the idea of philosophical optimism?

This is a complicated question ... I'll try a simple
answer and hope it's adequate.  Candide is a response to Gottfried Leibniz's assertion
that we live in "the best of all possible worlds."  Simply put, his reason was that an
all powerful and all good God could not create a less than perfect world because this
would make God less that perfect."

Candide is presented as
a sheltered young man who, accompanied by his tutor Pangloss, whose mantra is "all is
for the best in the best of all possible worlds," comes to experience a world that is
quite different from this mantra. There are historical events mentioned in the book that
would make one wonder how this could possibly be the best of any world, never mind the
best of all possible worlds --- the brutal Seven Years War and the Lisbon earthquake are
often cited as examples.

All this is motivated by
Voltaire's endless attacks on organized religion and repressive governments.  To believe
that this was the best of all possible worlds would have meant two things, the first
being that you weren't observing what was really going on, and the second that if you
thought this was the best, you might not be willing to put forward the effort to change
it.