Basically a condenser dryer extracts water from your clothes and deposits it in a reservoir.
It is a closed system where air is blown over a heating coil and into the tumble drum. It is then expelled into a condenser chamber where water is extracted.
With a basic vented dryer – the moisture is vented outside and the cost is less.
If you are after gentle drying you may like to look for a model with a drying rack.