Use of a claw hammer
Upholstery Hammer
An upholstery or tack hammer is used to fasten the upholstery fabric to furniture frames using small nails. However, the method of tacking in recent times has been replaced by a staple gun.
Any hammer is a meant to deliver a blow which may vary in intensity according to the type and utility of the hammer. Hammers necessarily have some basic parts which include a handle, a head which can be further classified into sub-parts - eye, cheek, neck, bell, face, peen/claw.

Although most hammers are simple hand-tools, there also exist mechanical hammers. Jackhammer, steam-powered hammer, hammer drill, high frequency impact treatment, trip hammer are some mechanically-powered hammers. These are used for heavy industrial jobs, but essentially work on the same principle of a hand-powered hammer.

Here's a list of 10 widely used hammers along with a picture of each. Also, read about the purpose for which each one is used.
Claw Hammer
Claw hammer
The claw hammer is one of the most widely used hammers. It is used to pound and extract nails in wooden or concrete surfaces. A standard claw hammer weighs somewhere around 1 to 1.5 lbs with a steel head and a wooden/fiber/steel handle. The claw is curved with a v-shape slit which hooks to a nail-head in order to extract it.
Ball Peen Hammer
Ball peen hammer
As the name suggests, the peen in this case is rounded. This hammer is used by engineers to bend or shape metals and shut rivets. Handles can be wooden, or steel in some cases; whereas the head can be made out of high-carbon steel or alloy steel.
Cross or Straight Peen Hammer
Cross or straight peen hammer
Quite similar to the ball peen, cross or straight peens have wedge-shaped peens instead of round ones. The peen of these hammers can either be perpendicular (cross) or parallel (straight) to the handle, the handle is mostly made up of ash wood. A cross or straight peen hammer is mostly used to shape metal.
Sledge hammer
As compared to the previous hammers, a sledgehammer is mostly used for heavy jobs. These may include breaking concrete, stones or for masonry. The sledgehammer can weigh up to 14 lb, and has a long (1.8 to 3 ft) wooden handle to facilitate better torque. It needs to be held by both hands unlike small hammers and needs to be swung like an ax for effective impact.
Club Hammer
Club hammer
Also called lump hammer, is a domestic hammer used in masonry mostly to drive nails and pound chisels. It can be used as a tiny sledgehammer to break stuff, and is commonly spotted at construction sites. These hammers typically weigh somewhere around 2-3 lbs and have a stout wooden handle.
The mallet is made completely of beech―a type of hardwood―and is used to pound and drive a chisel or connect wooden joints. It is typically useful in carpentry, especially where a metal hammer is prone to cause damage.
Geologist Rock Hammer
Geologist rock hammer
These are small hammers used typically by geologist and paleontologists to study rocks and fossils. The peen is pointed and sharp and is used to separate fragments of rock, whereas the head is flat and is useful for breaking small stones and pebbles.
Roofer Hammer
Roofer hammer
The roofer hammer is used to fix slates on a roof. It has a pointed peen and a flat face; the former helps to create nail holes in the slates, whereas the latter is used to pound the nails down in order to fasten the slate. It also features a claw on the cheek (middle) which is used for plucking nails.
Drywall Hammer
Drywall hammer
A drywall hammer has an axed-shaped peen which does the work of cutting or making holes into drywall (plasterboard) to locate water lines in order to mend leakage or seeping. They can also be used to make holes in the plasterboard for other purposes. The flat face is used to drive nails into the drywall.
Power Hammer
Power hammers
Power hammers, as mentioned above, are based on the same concept as that of regular hammers. However, these are used for heavy jobs which can't be accomplished by small hand held hammers, such as forging iron for machinery, breaking up roads or concrete, and mining. (The image shows a jackhammer being used to demolish a road.) Power hammers may run on electricity, fuel, and even steam.
Other Types of Hammers
Apart from all these carpentry, masonry, and construction-related hammers, there exists other hammers which are used for completely different purposes. Two examples of these can be seen in the images below.
Gavel Hammer
Gavel hammer
A gavel is a type of mallet mostly used to signify authority of a presiding officer, especially to maintain silence and order in a meeting or proceeding. The gavel, in most cases, is accompanied by a sounding plate or block (wooden) upon which it is struck in order to enhance its sound quality.
Reflex Hammer
Reflex hammer
It is used by orthopedic doctors to check tendon reflexes. Likewise, there are several other variants in reflex hammers used for similar purposes. The one shown above is a Taylor reflex hammer.
Hammers, right from the Stone Age, have been tools of great utility for mankind. Modern hammers are constantly evolved forms of traditional rock and bone hammers; their utility cannot be substituted by any other tool, and therefore, are vital for several mechanical tasks.