What is the difference between the perfect/imperfect/preterite tenses?

All three of these indicate actions which occured in the past, but vary depending on duration.

The perfect tense ( he hecho) is used for past events which have just happened and are relevant to the speaker in the present.

The imperfect tense (hablaba/comia/dormia) is used for past events which were repeated and are relevant to the speaker in the present.

The preterite tense is used for past events which occured in a closed time period, these can be single events, or repeated over time BUT the duration must be clearly defined and cannot continue into the present.