I'm under the impression that slavery existed in Europe widely prior to the year 1000, excluding in the middle east and north Africa where it remained slightly longer. When and how would slaves typically be taken by slave traders? and what did slaves actually do when they were traded? Were they used for manual labour only or a variety of tasks?
Slavery did exist in Europe prior to 1000. There is evidence of this throughout the British Isles and Scandanavia- they were frequently taken in battle.
As to their uses- it's perhaps more accurate to look at widespread slavery as closely related to and overlapping with 'unfreedom'. The statistics and sources for this are pretty terrible. People could be bought and sold but were not attached to the land (this supposedly changed with the Norman Conquest). There was a limited lordship bond- the lord would provide food, for example- but freemen obviously had far more rights. The line blurs somewhat between slaves and unfree people with a few more rights and freemen and so on: but here are the basics, for pre 1066 England:
As I understand it, in Anglo-Saxon England pretty skilled people might be slaves. There were plenty of people to do general agricultural work, even for free. A lord's tenants might have to do weekwork. Slaves were often specialists therefore. There seems to be evidence (I think from the Domesday Book) of ploughman especially begin slaves, but also swineherds, beekeepers, and even a priest.
Often they were sold by Scandanavians. At other times they sold themselves, or were slaves as a result of penal slavery.
Edit: formatting