Anything from simple cuts to amputations. Most barbers would have spent time on the battlefield, where they would have learnt (possibly the hard way for those he treated) and gained experience on a huge range of cuts and wounds. But do not worry; if the flesh did not get better and turned bad he could always use his maggots to clean the wound.
Yes your local Barber was a man of many trades, including wig maker; well he had all the requirements on the floor of his shop after cutting everyones hair!
There was no National Health Service in the 17th Century like we have today, so getting medical treatment was both costly and difficult. The average life expectancy was just thirty-eight years, and there was a high mortality rate for children. At this time towns were becoming more and more populated, and people knew little about health and hygiene. People did not wash very often, waste was disposed of on the streets, and clothes were beaten rather than washed. This meant that rats and flies were commonplace on the streets, allowing disease to spread easily and quickly.
Most people, especially in rural areas, consulted a midwife, who would have some knowledge of medical care and remedies. Women could not practice medicine at this time, so most learnt their trade from their mothers. However, midwives were associated with witchcraft, which hindered their status as a recognised medical practitioner.
Surgeons were also beginning to take an interest in childbirth, which provided a regular source of income. They began to invent technical devices to speed up delivery and improve the safety of mother and child. It was Peter Chamberlen who invented obstetric forceps. Dutch doctors also became experts at Caesarean Section. All this meant that doctors became more popular than midwives, who by the end of the 17th century were reduced to practicing among the poorer classes and post-natal nursing care.