Jesus addresses people praying as another example of doing religious things to impress people (Matthew 6:5-8). He talks to the crowd about praying in secret (in the closet); praying using meaningful words and phrases (not repetitious words); and God’s knowledge of knowing the needs of His people.
The Bible has many examples of people praying. When taken as a whole, how would someone summarize these prayers and their purpose? Simply stated, it is people speaking to God about various thoughts they have, which might include thanksgiving, any request especially for forgiveness, or praising God for who He is, what He has done and His various characteristics.