This parsha begins the day after Yom Kippur, which was the day Moshe Rabenu came down from mount Sinai with the second set of luchos, as recorded at the end of Parshat Ki Sisa, (last week's parsha).
In the first aliyah of Vayakhel, Moshe gathers (the word "Vayakhel") the Jewish people and starts telling them G-d's commandments. He begins with the commandment of rest on Shabbos and of not lighting a fire on it, followed by the commandment to donate toward the building of, and to the actual building, of the Mishkan (sanctuary), its vessels, and the holy garments of the Kohanim. (We learned about the requirements of the building of the Mishkan, and of the garments of the Kohanim, in the recent Parshiyot.)
Rashi says that the commandment of Shabbos precedes the one about the Mishkan to show that resting on Shabbos supersedes the building of the Mishkan.
In the second aliyah the men and women come forward and donate to the building generously of their free will. They bring gold, silver, and copper, and blue, purple, and scarlet yarn, and stones for the Choshen Mishpat (breastplate of judgment), and spice and oil.
In the third aliyah, Moshe gives over G-d's choice of the skilled craftsmen to do the actual work: as we learned in last week's parsha. They are Betzalel and Oholiav as his assistant. They start construction, and the people continue donating generously, until the craftsmen report to Moshe that they have more than enough material for the building. Moshe then proclaims throughout the camp for people to cease giving for this purpose, as there is enough material.
In the fourth aliyah the craftsmen continue building the Mishkan with the material previously donated, and build the Mishkan according to the instructions Moshe heard on Mt. Sinai. In this aliyah the curtains and clasps of the Mishkan are made.
The construction of the Mishkan continues in the fifth aliyah, including the making of the boards and sockets of the Mishkan, and the Aron hakodesh (the ark for the luchos [tablets]), and the ark cover and the Poreches (the veil before the Kedosh Kedoshim (Holy of Holies)).
In the sixth aliyah, Betzalel makes the six-branched menorah (candlestick) and its vessels. Here, he also makes the "Mizbeach-Haketores" (the special altar for burning incense), and the holy anointing oil and the incense.
In the seventh aliyah Betzalel makes the altar of the burnt offerings. He makes the wash basin out of copper, from the mirrors of the women. At first, Moshe didn't want to use these mirrors because they represented the women's vanity in adorning themselves, but G-d treasured them more than anything else because the women used these mirrors to attract their husbands when they were fatigued in their slavery in Egypt. These lavers were to be used in the Sotah ceremony to make peace between a husband and wife. The Alter Rebbe - Rabbi Schneur Zalman of Liadi explains that the offerings for the Mishkan included gold, silver, and copper, but nothing sparkled except for the mirrors presented by the women.
Although, these lavers were the last articles of the Mishkan to be made, they were nonetheless the first articles to be used at the starting of every sanctuary service for the washing of the Kohanim.