You need three types of materials to build a fire: tinder, kindling, and fuel.
Tinder is dry material that ignites with little heat–a spark starts a fire. The tinder must be absolutely dry to be sure just a spark will ignite it. If you only have a device that generates sparks, charred cloth will be almost essential. It holds a spark for long periods, allowing you to put tinder on the hot area to generate a small flame. You can make charred cloth by heating cotton cloth until it turns black, but does not burn. Once it is black, you must keep it in an airtight container to keep it dry. Prepare this cloth well in advance of any survival situation. Add it to your individual survival kit. (How to make char – see below.)
You will need some prepared tinder. This can be almost any dry natural vegetable fiber. Cotton, linen, jute (burlap), sisal, hemp, or weeds from the field all work. A mixture of two fibers kindles more easily than any one fiber. Cotton and jute is an excellent combination. You need a wad about the size of your fist. It is best shredded fine and well mixed. When we were young it was common to use dryer lint. This worked really well at the time, but can no longer be recommended. With modern synthetics, dryer lint is likely to contain at least some polyester or other plastic. The fumes from many modern synthetics are TOXIC. Holding a wad of smoldering tinder under your face and taking deep breaths to blow harder is a BAD THING if there is any plastic in the wad.
Kindling is readily combustible material that you add to the burning tinder. Again, this material should be absolutely dry to ensure rapid burning. Kindling increases fire’s temperature so that it will ignite less combustible material.
How to Make Char – Simply put, the traditional char is cloth that has been made into charcoal. It is heated at high temperature in the absence of oxygen to drive off flammable solids in the form of gas, leaving a black cloth which catches and holds a spark, smoldering with a hot ember rather than flaming. Making char cloth is not difficult. All you need is a can that won’t melt in the fire, and some cloth. I use a steel 35mm film canister, but smaller and larger ones will work quite well, anything from a lozenge box to a paint can. The lid needs to fit tightly. Obtain a proper size can and punch a 1/16 inch hole in the lid. The best char cloth is made of heavy gauge cotton cloth, something like T-shirts, old towels, “terry” cloth and the like. Cut the cloth into squares of two inches, or so, and put them in the can loosely, not stacked tightly. Fill the can, but not so much as to compress the squares. Put the lid on and set the can in an open fire. I like to set it on coals so it will be stable. As the can heats, you will see gases or smoke begin to stream from the hole in the lid. They may catch fire, from time to time. When smoke stops coming from the hole, drag the can off and let it cool. If you open it too quickly, the rush of oxygen will cause the cloth to burst into flame, and you’ll have to start over. Once the cloth has cooled, examine it. Good char cloth is black, but still has a lot of strength. It should not fall apart from ordinary handling. If it’s more like black ash than black cloth, you cooked it too much. If the squares are brown instead of black, or if it is obvious the cloth hasn’t been heated evenly, put the top back on and cook it some more. Extra effort to make good char now will pay dividends when you put it to use.
Spark – The direct spark method is the easiest of the primitive methods to use. The flint and steel method is the most reliable of the direct spark methods. Strike a flint or other hard, sharp-edged rock edge with a piece of carbon steel (stainless steel will not produce a good spark). This method requires a loose-jointed wrist and practice. When a spark has caught in the tinder, blow on it. The spark will spread and burst into flames. Agate, carnelian, jade, bloodstone, chalcedony, quartz, and chert all work well. Any hard stone, which fractures to a sharp edge, will do the job. Keep your striker with you and when you see an interesting stone, try it.
If you like to travel prepared get a magnesium block. Here’s a picture of the emergency kit 
I carry in my purse which includes a magnesium block and a Swiss Army knife. It’s easy to scrape some magnesium off the block and use the steel strip on the side to create a spark with the penknife. It burns fast and very hot and will light dry tinder very quickly. You’ll see I also carry a flashlight and a whistle in case I need to the attract attention of someone out of ordinary earshot.
Note: I carry this set in office buildings too. I am always reminded that 9/11 caused power outages and visibility difficulties within the tower blocks. Having a flashlight with me ensures I can see my way out. The whistle is in case I get trapped and need to attract attention. It requires much less physical effort than calling out.
Fuel in the wild is most likely to be old wood. The best is dried out. So look under rock overhangs and in sheltered places for fallen branches or old fenceposts. Wet wood is tough to build into a roaring fire so you’ll need lots of other flammable material like dry leaves to coax it into flame. Build from thin to thick wood.Expect a lot of smoke!