Short answers, pulled from the story.
A hammer is a tool with a weighted head on a long handle, swung to deliver an impact to a small area. It is used to drive nails into wood, shape metal at a forge, crush rock, and for a wide range of driving, shaping, breaking, and non-destructive striking applications in trades such as carpentry and blacksmithing.
The use of simple hammers dates to around 3.3 million years ago, based on a 2012 find by Sonia Harmand and Jason Lewis of Stony Brook University near Kenya's Lake Turkana. The hammer's archaeological record suggests it may be the oldest tool for which definite evidence exists.
A claw hammer is a framing tool with a claw used to pull nails out of wood. It is commonly found in household toolkits across North America.
A hammer is a simple force amplifier that converts mechanical work into kinetic energy and back. When the head is stopped over a very short distance at impact, the stopping force becomes far greater than the original muscle force, by roughly the ratio of the swing length to the stopping distance, enough to bend steel or crack stone.
Titanium hammer heads are lighter than steel, allowing longer handles, higher head velocity, and the same delivered energy with less arm fatigue. A titanium head returns about 3 percent recoil energy, compared with up to 30 percent for a steel head.
The hammer appears in many symbols, including the hammer and sickle of the former Soviet Union, where it represents the industrial working class, and the hammer and pick of mining. In mythology, the Norse god Thor wields a hammer named Mjolnir, and the Celtic god Sucellus and the Greek hero Hercules also carried hammers.