Freemasonry can be seen as a beautiful system of morality, veiled in allegory and illustrated by symbols. The symbolism is mainly, but not exclusively, drawn from the manual tools of stonemasons - the square and compasses, the level and plumb rule, and the trowel, among others. A moral lesson is attached to each of these tools... The meaning of the symbolism is taught and explored through ritual. - from Wikipedia
Here are some links to websites with information about Freemasonry.
Masonic Lodge of Education
The Masonic Lodge of Education includes an extensive list of symbols and their meanings: (http://www.masonic-lodge-of-education.com/freemason-symbols.html).
The Masonic Apron
Each initiate, upon entering the Order, receives a symbolic apron, which is to be worn during all Masonic meetings and rituals.  This article shows the Masonic apron of Meriwether Lewis and explains the meaning of its rich symbolism.