Clothes are a really useful way of keeping warm. On a bike the wind speed is higher but your workrate is quite high so you need slightly different clothes to pedestrians. Generally you need to wear less so you are a bit cool before the ride. It is important to take some extra insulation to keep warm when fixing mechanicals and flats.
Windproof outer layers are vital but waterproofs are needed in the rain. Extremeties need protecting and all gaps should be sealed. Synthetic wicking garments are good but many of us are returning to wool for a much more comfortable ride. The great unsolved problen for winter riders is footwear.
In the summer, the increased windspeed on a bike increases the rate of cooling so heat is less of a problem than it is for walkers.