At first glance the Talmud appears to be an expanded commentary to the Mishnah.
The sages of the Talmud are referred to as amoraim, a term literally meaning "translators."
Indeed, a considerable portion of the Talmud does consist of textual and other exegeses of the Mishnah.
In reality, however, the Talmud is as old as the Mishnah itself, constituting the theoretical framework underlying the final rulings formulated in the Mishnah.
Moreover, unlike the Mishnah, which is primarily a code of law whose primary purpose is to instruct the individual or the Jewish community how to act, the talmudic discussions are essentially theoretical and are directed toward clarifying the basic principles of the law and the different schools of thought therein.
Practical inferences are considered essentially derivative, secondary conclusions drawn, for the most part, from the abstract discussion.
–Rabbi Adin Steinsaltz
From The Strife of the Spirit, p. 80, by Rabbi Adin Steinsaltz