A longship is a kind of galley, with both sails and oars. It is the type of ship that had been invented in Ancient Egyptian times and been in use by all peoples ever since.

Many people connect longships with the Vikings in their minds, but the Vikings were only one of many people who had longships. The Ancient Greeks had longships (called triremes) and so did the Romans. The Saxons used them as well.

So there is nothing special about a longship belonging to a Viking other than they did tend to be narrower and so faster than many.

The purpose of the sails and oars was that the sail could be used for most of a journey, with the oars being used close to the coast for better manoeuvring and also for a burst of speed.