What is Okurigana?

Okurigana are nothing new. It is the same old hiragana characters accompanying Kanji. It shows the grammatical functions of the word.
For example, if a verb such as tsukau is written in kanji as 使う. Do you see the final hiragana letter u? It is Okurigana!

Okurigana can also be used for various purposes such as showing verb and adjective conjugations. They also help the reader to distinguish between various kun'yomi for the same kanji. Okurigana are normally written in hiragana.
What okurigana to use with what kanji is fixed by certain rules of disambiguation.
Read Wiki's Okurigana for more!

Reference: www.sljfaq.org
Image courtesy: wikimedia