Salt preserving:

Back in the old days when there were no refrigerators to store food people used salt to preserved the food. As the demand for salt has increased, people took up jobs in order to get paid in the form of the salt, hence the name salary has originated. 

How does salt preserve food? In general, when we say we are preserving something, we are trying to keep the food away from microbial growth. When food is kept in a salt solution we have made the surrounding hypertonic to any cell to survive (cells lose water in a hypertonic water and shrivel), hence there won't be any growth of microbes and thus the food in salt will be stored. The same occurs with the sugar, which we use to preserve fruits in the form jams.

For more preserving methods and more information please watch the video: