This is a question get asked a LOT, and I mean a lot. Many people have certain preconditions about Freemasonry, most come from sources such as films based on the subject - The Man Who Would Be King (starring Sean Connery and Michael Caine), From Hell (Film starring Jonny Depp,based on a fantastic graphic novel by Alan Moore) or books, ranging from the famous anti-masonic books by Stephen Knight, to Dan Brown's conspiracy-laden Solomon's Key.
The truth is that being a Freemason is a personal commitment (note the word personal here), its a commitment to follow the ancient precepts of the order (such as Brotherly Love, adhering to the ancient landmarks and conforming to the particular customs of Freemasonry), a commitment to studying moral law and applying it in your day-to-day life, a commitment to our fellow man (not just Freemasons!, as some anti-masonic writers would lead you to believe), to show a kindness and generousity to our fellow travelers in this world.
There are three great Principles related to the moral teachings of Freemasonry:
Brotherly Love -
To show tolerance and respect for the opinions of others and behave with kindness and understanding to our fellow man. This sets a masonic attitude out as being very different from what can be perceived as the 'norm' for the world. We as Masons dont give up our rights to have opinions, whether religious, personal or political, but we learn to enage members of society in dialogue about these issues in a non-confrontational way. In otherwords we "dont fall out about our differences".
Freemasons are taught to show charity and care, not just for Freemasons, but for society as a whole. We don't see ourselves as a 'special' group who adicates from the needs and purposes of society, but we see ourselves as an integral part of society. We seek out those who are in need, and attempt to help them.
Freemasons strive for truth, that's a broad general statement - truth can be personal, universal - or both! There are many ways to search for truth - through study sacred text, through contemplation...