How to wash your car well?
When the surface of your car gets dirty, it needs to be cleaned. Cleaning liquid (shampoo) is used to increase water absorption and add a fat dissolving agent with much lower surface tension. When you apply this combination of water and shampoo to a dirty surface, the cleaner will loosen the dirt, weaken the adhesion of grease and/or dirt, and mix the dirt with the cleaner.
When you rinse your glove in the bucket with "rinse" water, the dirt will be released from the microfibers of the glove and discharged into the water. To some extent, you might conclude that washing is about safely transporting dirt into the water, where it's easier to remove.
Method of washing the 2 buckets.
There are several methods of washing, but one of the most widespread is the 2 bucket technique.