I have 1 red spot on the roof of my mouth, its really sore, when I swallow it hurts, and a lot of people I know are smokers, what can this be?

Hard to say. There is no way to diagnose a clincal lesion over the internet. Please seek the help of a local dentist. Your lesion could be anything from a canker sore, to an oral abcess, to an abrasion, to oral cancer, or something else. The sooner that you are seen the better.. Take care...
Many things. This could be several things from a lesion, salivary gland issue to an infection. Have a dentist evaluate you. Yes smoking is a risk factor for oral cancer. Please see your dentist.
Possibly and ulcer. You may have an ulcer. Any break in the lining of the digestive tract exposes the underlying layers of the digestive tract. If it is not gone in 10-14 days you should get it looked at by a physician or dentist.