In other words, do well on this day, and you'll be a happy candidate with a strong shot at your party's nomination.
Note that this otherwise excellent video has one misleading statement: when it says "it all started with Georgia's Secretary of State Brian Kemp," it's referring only to this election, not previous Super Tuesdays).
In most states, delegates are allocated proportionately based on the results of the primary or caucus (although a handful of Republican primaries, like in Florida on March 15, are winner-take-all contests).
Most Super Tuesday states allocate their delegates proportionally to the candidates who win either 15 percent or 20 percent of the vote (depending on the state and party). In other words, each state divvies up its delegates proportionally among the candidates who exceed the threshold. For the Republican race, with five candidates in the running, there's a good chance that not everyone will surpass the required threshold in certain states, which means means having to forfeit any earned delegates.
Most delegates in each party are "pledged," meaning they're mandated to support a particular candidate at their party's national convention in July. However, each party also has a certain number of "superdelegates" who, in theory, at least, are free to support whoever they want.
And lastly (because this isn't confusing enough), a primary or caucus is considered "closed" when participation is limited to only registered members of that party, "open" when participation is open to all registered voters, and "mixed" when independent voters are allowed to participate.
Here's a great explanation of the whole confounding process (from none other than a British news service):
Delegate count (AP)
The candidates (AP)