Laptops and notebooks are the same. They usually have a larger screen and a cd/dvd drive.
Netbooks are smaller and lighter, with a screen under 11", no cd/dvd drives and usually a slower processor and smaller hard drive. Some have a flash drive instead of a HDD.
Laptops/notebooks can be a desktop replacement and some have very poor battery life and are bulky to carry around.
Netbooks are designed for surfing the net on the move and emails. Many have very small keyboards making them unsuitable for typing long documents. Some netbooks run on Linux instead of Windows.