Several things happen in Genesis 17.
This appears to be the first time that God has self-identified as El Shaddai, which the Amplified Bible defines as the all-sufficient one and the Common English Bible notes as God of the Mountain.
God changes Abram’s name to Abraham. Abram can be translated as “exalted father” and Abraham as “father of a multitude”.
Sarai’s name is also changed to Sarah. The Amplified Bible defines Sarai as “my princess” and Sarah as “Princess”, which seems like very little difference. The Amplified also has a note that offers an explanation that makes the difference more significant. In the Talmud the rabbis have commented “At first she became a princess to her own people, but later she became a princess to the entire world.”
These name changes seem to go along with God’s continued promise of a son to the two of them. This time though, the promise is to be fulfilled within a given timeline; “this time next year”. They have been waiting a long time for this to happen. Ishmael is 13 years old, and they went the way that led to his birth to fulfill the promise after they thought they had already waited too long for God to act.
Circumcision is established as the sign of the covenant. So Abraham is circumcised at age 90, and all of the males in his household (which includes servants) are circumcised as well on the same day.