Nature Transformation

The Five Basic Elements
Most Ninjutsu techniques are based on five basic elements borrowed from the environment:

Katon (Fire Element)

Suiton (Water Element)

Fuuton (Wind Element)

Doton (Earth Element)

Raiton (Lightning Element)

And when a technique utilizes an element independently, it's often labeled with the name of the element at the beginning of the technique name. For example:

Katon: Goukakyuu no Jutsu (Fire Element: Great Fireball Technique)

Suiton: Suiryuudan no Jutsu (Water Element: Water Dragon Missile)

Translations may vary (Earth Element; Earth Style; Earth Release. It's all the same). These five basic elements have determined the names of the five great shinobi countries (see Naruto geography) depending on their specialty. However, this doesn't limit a shinobi from a certain country to use an element that is not local to that country. Like Hatake Kakashi, a typical Konoha Jonin who is most suited for Lightning techniques.

Shinobi Element Orientation
Elemental techniques are considered chakra-nature-manipulation techniques, because they change chakra, which a pure form of energy, into a certain element from the previous five. Each shinobi individual is oriented to a certain basic element, regardless of what country he belongs to. That can be tested using special prepared paper, holding that certain paper for a handful of seconds will reveal the holders orientation. That is by the occurrence of a certain change of the form of that paper, from being cut in half, to bursting into flame. The orientation of a shinobi to a certain type means he's most suited to that type. And thus would have more outstanding abilities if specialized in that type. Most Jonins master at least two basic elements. Like Captain Yamato, who masters both Earth and Water techniques well. However, Jonin with special cases like Hatake Kakashi, he masters Fire, Water, Earth and Lightning, mainly because of his possession of the Uchiha clan's Sharingan. Whether he is capable of executing wind techniques or not is still unknown.

Blending Elements
In Naruto Shippuuden anime episode 55, blending elements was explained. For some Ninjutsu are far too complex to be executed using one element alone. So, with the utilization of two different basic elements, a shinobi can execute a new, combined elemental technique. There are two known combinations of elemental techniques:

Suiton & Doton

Mixing Water and Earth styles together results in executing a Mokuton Jutsu (Wood Element), which was formerly used by the First Hokage, and currently by Captain Yamato.

Suiton & Fuuton

Mixing Water and Wind styles together results in what is called Hyoton (Ice Element). Used by Haku of the mist. It's also a common element amongst Yukigakure shinobi.

Unfortunately, Kakashi referred to mixed elements as Bloodline Limits (see Kekkei Genkai), and stated that he can't copy them with his Sharingan. However, in the first Naruto movie, Kakashi was able to copy Nadare Roga's Ice Techniques as if they were a normal element. That may be explained by the fact that Haku could create ice from his own chakra, whilst Yuki Shinobi only manipulate existing ice.

Light and Darkness
The existence of another dimension of elements was hinted to in the same episode, Yamato referred to it as Light and Darkness when Naruto asked about the element category that Nara's Shadow Techniques and Akamichis Size-multiplication techniques fall under.

Examples on Elemental Techniques
Fire Techniques:

Fire Element: Dragon Flame Technique

Fire Element: Phoenix Flower Technique

Water Techniques:

Water Element: Water Prison Technique

Water Element: Great Explosion Technique

Wind Techniques:

Ninja Arts: Cutting Whirlwind Technique

Ninja Arts: Dust Wind Technique

Lightning Techniques:

Chidori (and Chidori Current)

Raikiri (and Raikiri Double Charge)

Earth Techniques:

Mud Clone Technique

Earth Element: Inner Decapitation Technique