The basic cause for dandruff is that there is a overgrowth of skin cells leading to flakes. Ofcourse there are varying degrees of this condition. The most aggressive condition tends to have flakes that stick to scalp and bleed on coming out. Treatment for this would include topical application of certain medications an dmedicated shampoos.

There is no single reason for hair loss. Hair loss in the context of patterned baldness is largely genetic in nature. While hair loss in which there is a loss of patches of hair (alopecia areata) is an auto immune condition. Sometimes these conditions can be triggered or accelerated by stress or trauma. Hair doctors are the best to diagnose the exact cause and type of hair loss.

Well it depends on what kind of hair loss you are suffering and how advanced the same is. In case of patterned baldness while all the hair will not grow back, it is possible to stimulate growth of new follicles by external intervention.
Popular first line of treatment include oral and topical medications that are prescribed by dermatologists. The next line of treatment would be non surgical treatment where growth serums are injected into the scalp. The last line of treatment would be hair transplant.

Hair specialists or trichologists are best suited to deal with these problems and should be consulted before engaging in any treatment.

These are called Folliculitis. Colloquially these are also called Bal-Tod in Hindi or Heat Boils in English. This condition presents as red painful, pus filled boils. These can be caused by bacterial or fungal infections or by reaction to shaving, hair colour, oil massage etc. In all of these conditions it is recommended to show the same to a dermatologist of hair specialist who can advice on the correct oral and topical medications.

Damaged Hair or Rough hair is often a result of environmental exposure and can be controlled by good hair care routine. For a good hair care routine to show effect I believe one must give it at least a month.