First, you need to make sure it is legal in your jurisdiction. US federal law allows building firearms for personal use without a license with the exception of firearms covered by the NFA. These would be mostly fully-automatic firearms, short barrel rifles and short barrel shotguns. Check with the ATF for details. Making NFA firearms and any firearms for the purpose of sale requires a federal license. State laws may have additional restrictions.
Manufacture of firearms from scratch requires proper tooling, machinist skills, at least a basic knowledge of metals, some woodworking ability, and good firearms knowledge. Metallic ammunition reloading experience is a major plus. Firearms work with extremely high gas pressure. We are talking tens of thousands of pounds per square inch. A mistake can result in a catastrophic failure and severe injury. In short, if you don't know precisely what you are doing you'll shoot your eye out, kid. Or, blow off a finger or two.
An additional thing to keep in mind is that if you are making a self-loading gun, certain kinds of mistakes in design and/or execution of your project can result in something that can be legally recognized as a machine gun. Aside from being unsafe, building a machine gun without a license and ATF approval can get you some very real jail time, even in the US.
A safer way to go would be to build one from ready made components. In US this is very popular with M1911 pistols and AR-15 family of rifles. They require hand tools and patience to put together. In the worst case scenario you will wind up with a poorly functioning gun, but not with one that blows up. Keep in mind that a bare receiver or pistol frame is considered a firearm in the eyes of US law and their sale has the same requirements and restrictions as a complete gun.
There are also kits for making muzzle-loading firearms to be used with black powder. They are generally simpler than a more modern gun and could be a good way to acquire skills for more complex builds.
The actual building process is far beyond the scope of this website.
eat some cherry pie and say "aardvark" 17 times
You would need to get the set and view the directions.
A Machine
get some Lego and then build it simple as
They either buy it seperately or from a Lego set.
LEGO and brickarms are not connected, but brickarms makes their own LEGO guns that are compatible with LEGO especially the minifigures.
Only Space Rangers have guns.
If you go to www.brickarms.com they have increbidle Lego guns!(do not be discouraged by the prices($2-25 cents), they are AWSOME!!! Another website is www.brickforge.com, which makes guns as well as other minifig acessories.
follow the instructions and build!
To build Lego robots.
The Lego website has a Lego app that you can download to build different designs. The app is linked below.
You get a bunch of legos and build it.
you play it after you build the rocket in the Lego Indiana Jones 2.
you can build a computer;a house and a lego city