After one year from the ratification of this article the manufacture, sale, or transportation of intoxicating liquors within, the importation thereof into, or the exportation thereof from the United States and all territory subject to the jurisdiction thereof for beverage purposes is hereby prohibited. (18.1)
That's it, right there. A right, previously thought to be just fine, is gone. Poof. The Constitution had never taken away an individual right before (well, other than the right to be a segregationist), so this was a huge moment.
This article shall be inoperative unless it shall have been ratified as an amendment to the Constitution by the legislatures of the several States, as provided in the Constitution, within seven years from the date of the submission hereof to the States by the Congress. (18.3)
Each state legislature chooses whether or not to ratify the amendment. When ¾ of the states say yes, it's a done deal. That's one way to ratify an amendment.
This article shall be inoperative unless it shall have been ratified as an amendment to the Constitution by conventions in the several States, as provided by the Constitution, within seven years from the date of the submission hereof to the States by the Congress. (21.3)
The 21st amendment does things a little differently. Instead of sending the decision to the state legislatures, Congress ordered each state to appoint a convention that would vote on the Amendment. The convention could be made up of regular citizens. By handing it over to a convention, Congress is explicitly taking the choice from the hands of elected state legislatures and placing it in the hands of the people. This is the only time this method of ratification has ever been used. Seems that some members of Congress thought that some of the state legislators were a little too deep in the pockets of the temperance crowd.
The Congress and the several States shall have concurrent power to enforce this article by appropriate legislation. (18.2)
The Constitution was actually intended to guarantee rights rather than curtail them, and generally let the states do things like outlawing theft, murder, and so on. Seriously, murder's only a federal crime under certain specific circumstances (murder for hire, murder by mail, a bunch of others). Destroying mailboxes, stealing livestock, or flying a JetBlue airliner while drunk is a federal crime, but not plain old "I just killed a guy and he's not a judge or cop" murder. Anyway, even though the Amendment overrode state laws about alcohol, it allowed the states to work with the feds to decide how to handle enforcement. Seriously, though, who could compete with the Untouchables?
The transportation or importation into any State, Territory, or Possession of the United States for delivery or use therein of intoxicating liquors, in violation of the laws thereof, is hereby prohibited. (21.2)
In other words, Don't worry, South Carolina. Nobody's gonna make you re-open the saloons. 18 states voted to keep Prohibition, and about two-thirds of them gave their counties and towns a local option. After repeal, 38% of Americans still lived in dry towns (source).