Answer:
The same things we do now a days.
Not exactly. In the 17th century, the term "witch" was specifically applied to those who used magic to cause harm. Those who used magic in the way modern witches do were usually referred to as "wise-folk" or "cunning-folk". The term "witch" was rehabilitated in the mid 20th century, and now has a very different meaning to the 17th century usage.
Many old women were accused of being a witch, and many died an innocent death. For an example, If a lady were caught being a witch, or if she were accused of being a witch, they would tie rope around her stomach and put them in the water. If they floated on water, this obviously meant they were a witch because people believed witches were made of wood. If they sunk they weren't a witch, but they were dead anyway. This was a very unfair way to find out if somebody was a witch or not.
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The European Witch craze reallykicked off in the late 15th century with the publication of the Malleus Maleficarum by Kramer and Sprenger. Various bits of folk belief & medicine had been tolerated until then but as the Middle Ages saw faith being replaced by reason and the power of the Church undermined not least by new knowledge from the Islamic World (seen by the Church as devil worshippers anyway) the Church became increasingly oppressive. The belief in what witches did was probably largely defined by the beliefs of the persecutors rather than the victrims themselves.
In England the persecution was not by the Church but by the State. Of roughly 800 witches executed 80% were women & 20% men. Over 300 of these were hanged by Matthew Hopkins.& his henchman John Sterns in Essex.
In England torture had been officially abolished in 1640 and the confessions are often of incredibly trivial matters such as disputes over the price of herrings, whereas where torture was routine succh as Scotland & France victims confess to turning into cats, flying broomsticks, eating dead bodies from graves etc.
Witches did not really do any of this, but this reflects what the authorities thought they did. Many "wise women" or "cunning folk" were not accused but accused others of withcraft.
"Swimming witches" was done in the belief that holy water would reject a witch. If you sank you were not left to drown but pulled out. Even so many contemporaries did not believe in witchcraft - notably Jan Weyer who first coined the term "mental illness" to describe the victims confessions and Reginald Scot from Kent.
Most "modern" witchcraft is based upon the writings of Gerald Gardner or Alexander Saunders or Aleister Crowley. Gardner in particular claims to have resurrected 17th century paganism along the lines of the theories of Maragaret Murray. These have been extensively debunked by subsequent historians such as Professor Ronald Hutton (a man who says he was brought up as a pagan).
Currently people who imagine themselves to be witches are self-deluded if they believe their own brand of amateur dramatics represents any kind of historical continuity at all & if they do not make it up as thjey go along then they follow sonmeone else who does.