The word "torah" means "a teaching". The Torah is HaShem's (God's) teaching to the Jewish people. In the Torah HaShem tells us how to live. The Torah has many mitzvos (commandments) in it. They are HaShem's instructions to us. The Torah also contains stories. These stories are true and teach us about our history and our relationship with HaShem.
The Torah has two sections, the Torah Shebiksav (the Written Torah) and the Torah Sheb'al Peh (the Oral Torah).
The Torah Shebiksav has three parts:
All together there are 24 books, five in the Torah, eight in the Nevi'im, and eleven in the Kesuvim.
These three sections (Torah, Nevi'im, and Kesuvim) are frequently referred to by the acronym TaNaKh (or Tanach).
Many things are not explained in the Torah Shebiksav. Hashem gave the explanations to Moshe Rabbeinu on Mount Sinai together with the written Torah. These explanations are called the Torah Sheb'al Peh, the Oral Torah, because they were meant to be passed from teacher to student. In the years after the destruction of the second Beis HaMikdash (Holy Temple) there was a danger that the Torah Sheb'al Peh would be forgotten. Therefore, our Sages, led by Rabbi Yehudah HaNasi (The Prince), assembled a basic outline of the Torah Sheb'al Peh into a series of books called the Mishna. The Mishna was completed in the year 188 CE. The Mishna was intended to serve as a memory aid so that it would be easier for students to remember the Torah Sheb'al Peh. The Mishna was primarily an outline and did not include the in-depth analysis and explanation behind the laws. These explanations are called gemara. About three hundred years after the completion of the Mishna there was a risk that the gemara would be forgotten. Once again, our sages, now led by Rav Ashi and Ravina, compiled the gemara into a written work as a commentary on the Mishna. This completed work is called the Talmud. The Talmud is therefore the complete collection of the Mishna and the gemara.
The Talmud is made up of six sections. Each section is called a Seder (Order) and contains several books called Mesechtos (Tracts). The six Sedarim are: