In The Freudian Psychoanalytic theory, a person's personality is determined during that person's early childhood. Freud's theory is one that goes in a step sort of order. In his theory there are different stages that a person goes through, these stages do not flow, if a person gets stuck in one stage he/she can be stuck in that stage forever. Freud broke his Psychoanalytic theory into five psychosexual stages (although Barron's AP says four), The Oral, Anal, Phallic, Latent, Genital.
First is the Oral phase, this happens during early childhood and can stay with a person all the way up through adulthood. During this stage all objects of interest get put into the mouth. Examples of this would be a person biting his/her thumb or smoking excessively. Most people are out of this phase by the time they turn two years old.
Uh Oh, time to potty train, the anal phase now deals with the other orifice.
When kids are learning to use the bathroom, if they have a traumatic experience then it can change the way they think for the rest of their lives. Examples would be anal retentiveness or the complete opposite, absolute disorganization. This stage is usually over by the time the kid is three.
The phallic stage is where the young man or young woman now begins to form a sexual desire. The genitals are starting to develop and accordingly boys form an Oedipus complex and girls form another complex (similar to Oedipus, but I can not remember the name and I am trying to do this without looking in the book). The Oedipus complex causes the young boy to be jealous of his father for the love of his mother. This phase is usually over by the time the child has turned six.