How oracle db connection decides when more connection is needed

Oracle DB 19C

For Db connection string --> In Client linux machine :

1)How oracle db connection decides when more connection is needed

2)How often Incr Pool Size    create connections when needed (30sec 60 sec or due to what circumstance)

3)How often Decr Pool Size    decrease connections when needed (30sec 60 sec or due to what circumstance)