Theory:

When the crops are grown well and matured, they are ready for harvesting.
Cutting the matured crop is called, harvesting.
Harvesting season varies according to the type of crop (Rabi or Kharif) under cultivation. Harvesting method also varies from place to place, person to person and crop to crop.
 
Farmers harvest crops using a variety of tools. Some crops especially tea and coffee, are plucked with the bare hands, while paddy and wheat harvested using sickle. There are a variety of machines also available for harvesting such as thresher, winnower, etc.
 
Harvesting has two major processes such as threshing and winnowing.
 
Threshing:
The process of separation of seeds from the straw is called, thrashing.
The heaps of harvested crop is put on the threshing floor. A bundle is taken from the heap and threshed (or beaten up) using logs of wood. Due to the force applied, the grains get separated from the straw. Some times instead of beating the straw using logs, cattle are allowed to walk over the straw. Nowadays, thrasher, a mechanical instrument is used for thrashing.
Combine is a machine which does both threshing and harvesting.
A thresher :
 
Threshing_Machine By Ben Franske - Own work, CC BY-SA 4.0.jpg
 
A combine :
  
combine-harvester-Image by Hans Linde from Pixabay.jpg
 
Winnowing :
The process of separating the hay from the seed is known as winnowing.
After thrashing, the seeds are collected. Seeds covered here with hay or husk. Hay also need to be separated to make the seed/grain ready for cooking. 
 
winnowing.jpg

In the winnowing process, the seeds sprayed in the air or air is blown over the seeds to remove the husk. Seeds/grains are heavier, so they fall straight to the ground while the husk is blown away.
Reference:
Threshing Machine image: By Ben Franske - Own work, CC BY-SA 4.0, https://en.wikipedia.org/wiki/Threshing_machine#/media/File:Threshing_Machine_In_Action.jpg:
Combine image : Image by Hans linde from pixabay, https://pixabay.com/photos/combine-harvester-harvest-grain-4401822/
Winnowing image: By The Philosophy of Photography - flickr.com, CC BY 2.0, https://commons.wikimedia.org/w/index.php?curid=6846846