How do I start a fire?

If there is snow on the ground, build a platform with rocks or logs. Start with a pile of tinder. Tinder is small, dry, and easy to ignite such as grass, leaves, pine needles, or cloth. Light the tinder with a match or lighter. The sparks from a lighter can be used even if there is no butane and the tinder is easy to light such as dry grass. If there is no dry tinder, you may forcefully start a fire with a flare (I always carry a flare on search and rescue missions to quickly start fires for hypothermia patients). After the tinder is started, add tiny sticks. As the flame grows, add larger and larger pieces of wood.

If you do not have matches or a lighter, you can try to rub two sticks together. This is extremely difficult and takes practice. There are two ways to do this. One involves the use of a bow to rapidly spin a stick. The other involves rubbing a spiked stick down the groove carved into another stick. Both require a knife.

One thing to consider: If you are doing it properly, you will work up a large sweat. If you are unable to start the fire, your sweat will make you much colder later on. You should be fairly confident in you ability to start the fire if you are doing this in an emergency situation.

The bow method: Find a stick that can be bent into a bow. Tie a string (possibly a shoestring) to each end to make a bow. Carve a sharp point on each end of another stick.
Twist the stick into the string of the bow. Place a piece of wood in your hand and another on the ground. Place one sharp point of the stick against the wood in your hand and the other point against the wood in the ground. Move the bow slowly back and forth causing the stick to spin and drill a small hole into the pieces of wood. When you have good holes in the wood, start to vigorously spin the stick with the bow. When you see smoke, place the kindling near the smoke and blow.

Be careful not to injure yourself with the pointed stick near your hand. You can also use a straight stick and pull to maintain tension on the string.

The groove method (I think that's a song), also called a fire-plow: Carve a point on a stick of hard wood. Lay another larger sick of soft wood on the ground. Cut a groove down the length of the stick about 6 inches long. Place the point of the first stick into the groove of the second. Start to slowly move back and forth until the groove is well formed. Then start vigorously rubbing until you see smoke. Place the kindling near the smoke and blow. If you can't start a fire, you'll at least be warm from the effort.

There are other methods of starting fires such as flint & steel or steel-wool & a battery. These methods require that you have brought these items with you in anticipation of needing fire. However, most people would have simply brought a lighter if there was any forethought involved.