What is the main function of stomata?

Transpiration and role in respiration

There are two main roles of stomata:

First is the intake of carbon dioxide during day time for the process of while the givinng out of oxygen. At night time, the process is vice versa i.e Oxygen is intaked while carbon dioxide is given out.

Second is the taking out of water i.e transpiration. Just like sweating in humans, transpiration takes place in plants. Water leaves the plant body when it is in excess amount.