One at a time:
Vayyikra refers to the third book of the Bible known in English (actually
Latin) as Leviticus. 1:2 is the chapter and verse.
Sifra (this is a hard one) refers to a collection of ancient commentaries
on Vayikra. These commentaries are called beraisos and were, I believe,
compiled at about the same time as the Mishna. Um, the Mishna is the
ancient compilation of authoritative statements compiled by Rabbi Yehuda
HaNasi, it forms the framework for the Talmud. (I suggest you check the
section titled "What is the Torah?" on my website
BT stands for Babylonian Talmud. This is what is generally meant when we
refer to the "Talmud". The Talmud is made up of the Mishna and commentary
upon the Mishna called Gemora.
JT stands for Jerusalem Talmud. This was an earlier version of the
Talmud. While a very important work, it is less authoritative than the
Babylonian Talmud and therefore less studied.
Berakhot and Pesachim are tractates in the Talmud dealing with the laws
of prayer and blessing and the laws of Pesach (Passover) respectively.
>Also what is the definition of these words? Pirkei Avoth; Mishnayot;
Pirkei Avot is the name of a tractate of the Talmud which deals with
moral and ethical issues. It is probably the most studied tractate in the
Talmud. There is no Gemorah on Pirkei Avot, only Mishna (see above).
Mishnayot is plural for Mishna. In this case it doesn't refer to the work
of the Mishna as a whole but to individual statements of the Mishna, each
of which is itself called a Mishna. Mishnayot would be numerous
Magen/Mogen. I assume you are refering to the common usage of Magen or
Mogen David. It means Shield of David and refers to the six pointed star
commonly associated with Jews (as in the flag of the State of Israel). I
believe it has some kind of basis in Kabbala but I'm really not sure.
Good luck in your studies!
Eliezer C. Abrahamson