Multiclassing

Multiclassing allows you to gain levels in multiple classes. Doing so lets you mix the abilities of those classes to realize a character concept that might not be reflected in one of the standard class options. With this rule, you have the option of gaining a level in a new class whenever you advance in level, instead of gaining a level in your current class. Your levels in all your classes are added together to determine your character level. [...] As you advance in levels, you might primarily remain a member of your original class with just a few levels in another class, or you might change course entirely, never looking back at the class you left behind. You might even start progressing in a third or fourth class. Compared to a single-class character of the same level, you’ll sacrifice some focus in exchange for versatility. - SRD; Page 56

Multiclassing works differently to normal Dungeons and Dragons, since you cannot gain the ability to bend without the Lion Turtles gifting it to you, nor can you be a bender of more than one element, unless you are the Avatar. When phrased this way, it is recommended that if a player would like to bend in the future, they choose their class to be a bender, then multiclass later on. For example, if a character wanted to be a Fire Bending Ranger, they should choose Fire Bender as their original class, then multiclass into range; if they chose ranger initially, they would be unable to choose bender later on. As such, benders will not be included in any table below.