How do I know when to use the imperfect tense of the preterite tense?

Both the imperfect tense and the preterite tense are used to describe the past. However, they are used to describe different things. The imperfect tense is used to describe actions that happened repeatedly and over a long period of time. For example: "Iba al colegio en coche" (I went to school by car). Using the imperfect form of IR here ("iba") makes this sentence mean that I always used to travel to school by car. On the other hand, the preterite tense is used to describe actions that happened once and are now over. Using the same example: "Ayer, fui al colegio en coche". Using the preterite form of IR here ("fui") means that yesterday I went to school by car, as a single event that has now finished. Using both forms in one sentence respectively, an example could be: "En mi primer año de colegio venía al colegio en coche, pero ayer vine en autobús." This means: "In my first year of school I used to come to school by car, but yesterday I came by bus." It is clear here that coming to school by car was a repeated action but that the trip by bus was a one off.