To get started it is best to visit this website: www.letterboxing.org. The site is excellent and has everything you will need to know to get started, find locations all over the world and print off the necessary clues.
The next step will be to create your "handle", "character" or I.D. I found the best and easiest way was to visit the local craft store and find a rubber stamp that everyone likes. Some people like to make there own out of white erasers and you can find out how to do that by going here: http://www.mitchklink.com/letterboxing/carving.htm But for newbies, I'd stick with buying one for your whole family or one for each individual in your family. When we began five years ago, we were a family of five; hubby, three boys and me, so I chose a stamp with three Cootie bugs and made our name "Ima Cootie". To make it more special, we use turquoise ink when we leave our mark in a Letterboxing journal and usually leave a note like, "This was a fun one" or " What a great hike" with our "Ima Cootie", date and where we are from.
It's always a lot of fun to look through the journal to see who else has been there, what notes they leave and where they originated.
One of the fun parts about Letterboxing is the secretiveness. Most are placed where people walk by everyday and have never noticed a SPOR(suspicious pile of rocks) or a perfectly placed downed log. Some boxes we have found have even been in museums behind furniture or in crevices and supposedly the museum workers don't even know they are there, so it is imperative that you search very sneakily and when you find it, remove yourselves from the location to open it and do the stamping. Then very quietly and covertly put it back and secure it in it's original location so that others can find it just like you did.
Most of our road trips, vacations or days out include at least one letterboxing adventure which have taken us through the woods, in museums, historical and government buildings, lighthouses, rest areas, on top of waterfalls and even under benches and statues at the beach. There are so many things we would have never discovered or experienced together if we had not gone on these little treasure hunts. They keep everyone busy and excited when you've run out of other things to do.
Good Luck and Happy Hunting!