1) After eating and sleeping on Shabbat afternoon. 2) Exodus 35:1. 3) Midrash Yalkut Shimoni, Vayakhel. 4) The Midrash ends with Hashem declaring to Moshe that if the Jews do this (that is, learn and teach Torah communally on Shabbat) He will treat it as if they have made Him King in His world. 5) Jerusalem Talmud, Shabbat 15:3. 6) A Midrash quoted by the Tur (see Mishna Berurah 290:5) tells how the Torah said to Hashem: ''When the Jews enter the Land of Israel, this person will be running to his vineyard, this one to his field, what then will become of me?'' Hashem answered: ''I have a partner for you, who's name is Shabbat, and (on that day) they will be free from their work and will thus be able to engage in (the study of) you.''

1) Being called up to say the blessing which precedes each public reading of a section of the Torah scroll, is called an ''Aliyah''. On Shabbat, the weekly Torah portion is split into 7 sections and a different person is called up to say the blessing before each section is read. It is allowed to split the Torah portion into more than seven sections on Shabbat, and so call up more than seven people. If there is a Cohen in the synagogue, he gets the first aliyah, followed by a Levite. 2) A Cohen or priest is a direct descendant on the male side of Pinchas (the grandson of Aharon). 3) A Levi or Levite is a direct descendant on the male side from the tribe of Levi. The tribe of Levi was chosen to serve G-d in the Sanctuary because they did not take part in the sin of the Golden Calf. 4) The final aliyah is called ''Acharon''. 5) After the reader has read the entire weekly portion (usually completing it with the seventh aliyah), another person is called up and the last few verses of the portion are repeated; this final aliyah is called Maftir. 6) The Festival of Simchat Torah marks the completion of the yearly reading cycle of the Torah scroll (one portion per week). Three scrolls are taken out: one for the completion of the final weekly portion of the Torah, the second for the beginning of the new yearly cycle of reading from Genesis, and the third for reading the section of the Torah describing the sacrifices brought in the Temple on the Festival. 7) The concluding aliyah in the Book of Deuteronomy. 8) The opening aliyah in the Book of Genesis. 9) The first day of the Hebrew month of Tevet. 10) The final aliyah in the first Torah scroll. 11) Describing the sacrifices brought in the Temple on the first day of each month. 12) For the Rosh Hodesh aliyah. 13) During the four weeks leading up to Pesach, we read an extra paragraph from the Torah scroll on Shabbat besides the regular weekly portion - each from a different scroll. One of them is the paragraph describing the obligatory donation of money to the Temple each year, called ''Parshat Shekalim'', and another is a paragraph describing the Mitzvah of sanctifying the new moon, called ''Parshat HaHodesh''. See also Ch. 140.

כשמוסיפין בשבת יכולין לקרות כהן או לוי לאחרון כיון שכבר השלימו שבעה גברי וגם שהוא האחרון מעיקר הקרואים חוץ מן המפטיר וכן המפטיר יכולין לקרות כהן או לוי ואפילו כהן אחד לאחרון וכהן אחד למפטיר יכולין לקרות כיון שהקדיש מפסיק ביניהם ובשמחת תורה שמוציאין שלשה ספרי תורה יכולין לקרות כהן אחד לחתן תורה ואחד לחתן בראשית ואחד למפטיר כיון שכל אחד קורא בספר תורה אחר אבל בראש חדש טבת שחל להיות בשבת אף על פי שמוציאין גם כן שלשה ספרי תורה אפילו אם רוצים לקרות בספר תורה הראשון שמונה גברי אין רשאי לקרות להכהן שיהיה השמיני כיון שעדיין אין משלימין הקריאה בספר זה והמשלים הוא בספר השני שקורין בו פרשת ראש חדש ואז יכולין לקרותו וכן הדין בשבת שקלים ובפרשת החדש כשהם בראש חדש

1) By mistake. We don't normally call up a Cohen or Levi after the first two aliyot except for Maftir or Acharon. This is because if a Cohen was called up immediately after another Cohen the congegration may think that the first was disqualified in some way and for that reason we called up the second.