The volitional form of a verb, used to express intention, suggestions, or speculation (e.g., '行こう' meaning 'let's go' or 'I'll go').
来週は早めに出発しようと意向形で決めた。
I decided, using the volitional form, 'Let's depart early next week.'
先生はクラスで意向形の使い方を説明した。
The teacher explained how to use the volitional form in class.
「一緒に行こう」と誘うときは意向形を使う。
You use the volitional form when inviting someone, e.g., 'Let's go together.'