Generally speaking, the Talmud is the gathered Jewish oral Tradition that explains and interprets the Torah. The oral tradition remained oral until the second century A.D.; the process of gathering and writing down the oral tradition lasted until around the fifth century A.D. The Talmud consists of two major writings: the Mishnah and the Gemara. The Mishnah is the original commentary on the Torah; the Gemara is elaborations on the Mishnah.
Whether the Talmud will be helpful to you in understanding Christianity depends on how familiar you are with Judaism and with Catholicism. You also should be well-versed in what the Talmud is and how talmudic arguments are made. Certainly if you are already familiar with where Judaism and Catholicism intersect and if you have a good understanding of the Talmud, including its limitations, studying the Talmud may be immensely helpful. But if you do not have the necessary background, Talmud study for a Christian may be more confusing than helpful.
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