Our tradition tells us that God forgave the Jewish people for the sin of the Golden Calf on Yom Kippur.
The next day Moshe gathered the people and told them about the Divine command to build the Tabernacle (Mishkan).
From this parasha until the end of Sefer Shemot, the Chumash focuses on building and inaugurating the Mishkan (tabernacle).
The Mishkan is the portable temple that the Jews were commanded to build in the desert. It was disassembled every time they moved from one camp to another and then rebuilt.
The main part of the Mishkan was a tent that was divided into two sections – the Holy and the Holy of Holies.