Actually very little but loosely speaking the term of treatment and the depth of the counselor's (or psychotherapist's) training.
Although it varies between therapists, psychotherapy (or psychoanalysis as it used more commonly to be called) sessions are typically 50 (fifty) minutes long for individuals and 80 (eighty) minutes long for couples.
How long you continue having therapy for depends on how much you want to do.
Some people never stop having therapy – I have been having personal therapy for around twelve years. Others come with a specific problem they want to work on and stay only until they feel they’ve achieved that goal (for example learning to cope with a fear of flying or working through doubts prior to their wedding).
I think modern psychotherapy mainly benefits people who are struggling with emotional problems including (but not limited to) depression, anxiety, friendship / marriage / family, shyness, OCD, drugs / alcohol and gambling (and other addictions). Some people (like myself) continue psychotherapy for a very long time or throughout their lives, not to resolve personal problems but because the self awareness and personal changes that are possible through psychotherapy can become a hobby, an occupation and a way of life.
This is an excellent question and one that researchers have yet failed to conclusively answer. There is a good evidence that psychotherapy does work but exactly how is not yet known. There is a large (and growing) body of scientific research which suggests that most of the benefits of psychotherapy are in the quality of the relationship between client and therapist and from experience and this is the research I feel most closely aligned with.
Doing all of these things can be reasonable and helpful ways of working on your issues. Sometimes though, without us realising, it's our continued involvement with the people around us that perpetuates our problems. Through their lives, people tend to find friends and situations that reinforce their own style of relating. Further, that style of relating is usually learned in the family (in other words, the continued presence of family and friends who reinforce your unconscious ways of relating keep on causing you trouble).
There are many different psychotherapy techniques and psychotherapists' techniques differ depending on their training and personal views. My way of doing psychotherapy has come from my training, personal background and clinical experience. Here's what you can expect in therapy sessions with me.