Psychotherapy, often referred to as "therapy", is a kind of talking therapy which is meant to help people resolve various symptoms and understand themselves better. There are many kinds of psychotherapy. Generally, understanding more about your interior world, i.e. your mind and motivations and feelings, is helpful in successfully changing your behavior, which in turn, leads to a better life.
Some types of therapy focus on your thoughts, feelings, and behaviors in a surface kind of way and are usually short term solutions offered in a short term therapy. They typically focus on how you can change problematic thoughts and behaviors through various acts of the will, like choosing to think different kinds of thoughts, taking deep breaths, or choosing to behave in a different way. These kinds of therapy sometimes have homework or charts or various aides that you are asked to do or make or keep. Sometimes they involve advice from the therapist. These types of therapy don't usually try to look at the roots and deep reasons for your thoughts, feelings, or behaviors. Rather they focus on strategies to deal with them. Cognitive Behavior Therapy (CBT) is an example of this kind of therapy.
Other types of therapy focus more on understanding your thoughts, feelings, and behaviors in a deeper way. This may involve linking the present to the past or examining dreams and unconscious wishes, or "peeling away the onion" of the reasons for why we do what we do. Depending on the therapy, there may be an emphasis in one area or another. Psychoanalytic psychotherapy and psychoanalysis are two approaches to a deeper type of self understanding. These kinds of therapies are considered long-term therapies and often take months, sometimes years, to accomplish their goals.