Ki Tisa in a Nutshell

Exodus 30:11–34:35

The people of Israel are told to each contribute exactly half a shekel of silver to the Sanctuary. Instructions are also given regarding the making of the Sanctuary’s water basin, anointing oil and incense. “Wise-hearted” artisans Betzalel and Aholiav are placed in charge of the Sanctuary’s construction, and the people are once again commanded to keep the Shabbat.
When Moses does not return when expected from Mount Sinai, the people make a golden calf and worship it. G d proposes to destroy the errant nation, but Moses intercedes on their behalf. Moses descends from the mountain carrying the tablets of the testimony engraved with the Ten Commandments; seeing the people dancing about their idol, he breaks the tablets, destroys the golden calf, and has the primary culprits put to death. He then returns to G d to say: “If You do not forgive them, blot me out from the book that You have written.”

G d forgives, but says that the effect of their sin will be felt for many generations. At first G d proposes to send His angel along with them, but Moses insists that G d Himself accompany His people to the promised land.
Moses prepares a new set of tablets and once more ascends the mountain, where G d reinscribes the covenant on these second tablets. On the mountain, Moses is also granted a vision of the divine thirteen attributes of mercy. So radiant is Moses’ face upon his return, that he must cover it with a veil, which he removes only to speak with G d and to teach His laws to the people.

Source: http://www.chabad.org