The Garuda Purana has nineteen thousand shlokas. It is a medium-sized Purana. The Skanda Purana, for example, has eighty-one thousand shlokas. And the Markandeya Purana only nine thousand. The thousand shlokas of the Garuda Purana are divided into two parts, a purva khanda (first part) and an uttara khanda (subsequent part). Each khanda has several chapters (adhyaya). The purva khanda is much longer, it has two hundred and thirty-four chapters. The Uttara khanda has only forty-five.
The latter half of this Purana deals with life after death. The Hindus of India generally read this Purana while cremating the bodies of the dead. This has given great importance to the origin of Garuda. There are nineteen thousand verses describing the ways to the Lord.
The word Suta may refer to the Sutas, a class of people born of Brahmana mothers and Kshatriya fathers. These are two varnas of the Varnashrama system. The duty of Brahmans is to pray and study the sacred texts, apart from assisting in religious rites. The duty of Kshatriyas is to bear arms and protect the world.
The Sutas were neither Brahmanas nor Kshatriyas, they were children from intermarriage. Their duties were to look after horses and act as charioteers.
Vedavyasa taught the Puranas to one of his disciples name Romaharshana or Lomaharshana. He was thus named because the hair (roma) on his body (roma) was thrilled (harshana) when he heard the Puranas from his teacher. It was Romaharshana who related the stories of the Puranas to everyone else. The Bhagavata Purana says the Romaharashana had a son named Suta and it was this son who related the story of that particular Purana to the other sages . On the other hand, Romaharshana himself belonged to the suta class, so that he too could be addressed as Suta. From reading the Garuda Purana, one does get the impression that it is Romaharshana himself who is relating the story, and not his son.
To come back to the point, Romaharshana came to a forest known as Naimisharanya. He sat there and contemplated the mysteries of the Lord Vishnu.
Several other rishis (sages) led by Shounaka also came to the forest. They told Romaharshana, "Sage, you know everything. Who is the god of all gods? Who is to be worshipped? What does one meditate on? Who destroys evil? How did the world come to be created? What is dharma (righteousness)? Tell us all these things and more".
"I will", replied Romaharshana. "I will recite to you the Garuda Purana. Many years ago, this Purana was told to the sage Kashyapa by the great bird Garuda himself. I learnt it from my teacher Vyasadeva. But first let me list for you the twenty-two avataras of Vishnu.
The first incarnation was a young boy (kumara). In this form, Vishnu adopted celibacy (brahmacharya) and performed difficult tapasya (meditation).
The second incarnation was as a boar (varaha). In this form, Vishnu rescued the earth from the underworld.
The third incarnation was as a great sage (devarishi). In this form, Vishnu spread the knowledge of several texts (tantras).
The fourth incarnation was as two sages named Nara-Narayana.
The fifth incarnation was as the great sage Kapila. Kapila taught his disciple Asuri the wonderful philosophy known as samkhya yoga.
The sixth incarantion was as the sage Dattatreya, the son of Atri and Anasuya.
The seventh incarnation took place in the manvantra known as svayambhuva. Vishnu was born as the son of Ruchi and Akuti and performed many yajnas (sacrifices).
In the eighth incarnation, Vishnu was born as the son of Nabhi and Meru. His name was Urukrama. He taught everyone the righteous way of life.
In the ninth incarnation, Vishnu became the king Prithu and restored foodgrains and herbs to the earth.
The twelfth incarnation was as Dhanvantari, physician of the gods and the originator of medicine.
In the sixteenth incarnation, Vishnu became Parashurama, killed all the kshatriyas in the world twenty-one times.
Vishnu’s eighteen incarnation was as the sage Narada.
In the twenty-first incarnation, Vishnu became a Buddha.
The twenty-second incarnation is yet to come. And Vishnu will come. Vishnu will be born as Kalki, so as to destroy evil in the world and restore righteousness".
There have been several other incarnations of Vishnu. But the ones mentioned above are the major ones.