First of all, smoke represents a large number of participles (gas, liquid and tiny solid) and although it is built from hundreds of different chemicals, smoke that is visible to the human eye is consistant mostly of carbon, tar, oils and ash. In essence, smoke represents a collective of tiny unburned participles which occur when there is not enought oxygen to burn the fuel completely, leaving just water and carbon dioxide produced. Each participles, out of which smoke is consistant is perhaps too small for human eye to see it, when merged together with others it comes out as smoke. Smoke has a distinctive smell, taste and colour (which can vary from grey to black and even to chemically coloured.)
Smoke ninjutsu will allow user to manipulate pre-existing smoke to create offense and defense. Smoke within our realm acts as a poison, which will cause for one who inhaled it to suffer great amount of damage, stop breathing, suffocation and similar. One must keep in mind that smoke can affect themselves whilst manipulation, which means just because someone is able to manipulate smoke, doesn't mean they are resistant to it. That is the reason why smoke users use gas mask so to protect themselves. Due to inability to produce smoke from their body, users usually possess wrist launchers which will allow them to release smoke and then manipulate it further performing differing techniques. For this even smoke bombs can help or any kind of smoke sources. I'd like you two to tell me about gas masks, wrist launchers and smoke bombs. And any other ways to produce smoke if they come to your mind!
Next thing you must keep in mind is that smoke doesn't have upper hand against any of the basic 5 elements but is weak to water and wind. Wind will easily blow away smoke whereas water will soak down the participles from which it is created.