Russian imperfective verbs are most often unprefixed. Perfective Perfective verbs are reserved for actions that have been completed, or, at least, when the speaker wants to emphasize the completion of the action. This section will also be developed further at a later date. Some textbooks also call this actual vs. habitual. If you think of this set in both terms, it may help, because habitual is obvious - it's a habit that is done often, while determinate, for example, means that there is a previously determined destination.
Determinate verbs are the one-way, definite destination type.
It implies a habitual action and a round trip, because we assume that the speaker will also be returning from school. In Russian, the meani ng can be quite different. The former form means a one-way trip, on foot to school. The latter form means a habitual, perhaps round-trip variant, also on foot. Again, the best way for you to decide which verb to use is to complete the sentence you are creating as much as possible.