Instructions
Acquire LEGO Army Men Parts
Consider buying the classic, stylized LEGO Army Men, based on characters from the Toy Story franchise. Note that these minifigures, which resemble classic green army men down to the connected base at their feet, naturally lack realism, but they are easily purchased and assembled, and they are official LEGO brand products.
Look at aftermarket or secondary market military products, compatible with but not produced by LEGO, for more realistic or modern military figures and accessories. Browse these products through the links in the Resources section; they include authentic models of World War II and modern weaponry and armor.
Purchase certain older LEGO sets for reasonably authentic period military attire; for instance, the LEGO Indiana Jones theme and older LEGO Adventurers theme feature pre-World War II military uniforms.
Assemble LEGO Army Men
Use the various pieces you have acquired, from stylized army men, period uniforms and unofficial products to create your own custom LEGO army men. Assemble the minifigures first by attaching the legs piece to the torso piece, and then by attaching a head.
Outfit the minifigures as desired -- attach a hat or helmet onto the head and insert a gun or other weapon into the hands. Listen for a light click sound to make sure the piece is securely attached.
Customize the army figures as much as you want -- assemble the unofficial products as they are in-box for accurate World War II or modern era military figures, or mix and match between different sets to fulfill your own creative vision.