What is a collection?

A Meteor collection is a like an advanced Array object. To briefly illustrate what a collection can do, here are some use cases:

Teams = new Mongo.Collection('teams');
Teams.find(); // finds all your teams
Teams.find().fetch() // finds all your teams and returns them as JSON
Teams.insert({name: 'Team 1'}); // Inserts a team into Mongo
Teams.update({_id: id}, {$set: {name: 'Team 2'}}); // Update a team
Teams.remove(id); // Removes a team

Don't worry about memorizing it all - I'm just showing you what it can do.