In the sentence I had finished my homework before I practiced the piano, there are two separate past tenses that are employed: the past perfect tense and the simple past tense. Both of these tenses are in the Basic form.
Indeed, the two forms of the past tense do differ in their expression of time, or the ordering of events. The past perfect tense, for instance, indicates an action that occurred and was completed in the past prior to another past action. Thus, the verb had finished is in the past perfect tense. [a compound tense, with the Latin word perfect meaning completed]
On the other hand, the simple past tense indicates an action completed by itself in the past, or an action completed in the past after a prior action. Thus, the verb practiced is in the simple past tense [simple meaning one verb]. So, the author of the above sentence practiced the piano only after finishing the homework, the first action.