Theory:

When the crops are grown well and matured thy are ready for harvesting.
Cutting the grown up 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 are 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, thrashing and winnowing.
 
Threshing:
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 are separated from the straw. Some times instead of beating the straw using logs, cattle are allowed to walk over the straw. Now-a-days, 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 :
Separating the hay from the seed is known as winnowing.
After thrashing, the seeds are collected. The seeds are covered with hay or husk.  This also need to be separated so as to make the seed/grain ready for cooking.
 
winnowing.jpg

During winnowing the seeds are 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 and settled a bit farther.
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