The Little Entrance is the procession of the clergy to the altar led by the Book of the Gospels. It sometimes called the "Small" or "First" entrance.
If the priest is serving the Divine Liturgy alone, without a bishop, the Little Entrance is made by the clergy circling the altar table and then to the middle of the church with the Gospel Book. Then he enters the alter through the royal doors of the iconostasis accompanied by the Hymn of Entrance.
If the bishop is celebrating, the Gospel Book is brought out to him in the center of the church, in the midst of the people, where he has been standing from the beginning of the liturgy.
Originally, the Little Entrance marked the beginning of the of the service, but now it is preceded by various Litanies and Psalms. It was a way the bring the Gospel Book from where it was kept, to the service.