使え

In a sentence

• この道具は簡単に使えますよ。

  This tool can be easily used.

  Here, '使えます' is used in a declarative form to express the action of the tool being usable.

• 彼女にそれを使えと言われた。

  She told me to use it.

  Here, '使え' is a command form in reported speech, indicating an instruction to use something.

• 電波が悪くて電話が使えない。

  The signal is bad and the phone cannot be used.

  Here, '使えない' is the negative form, expressing the inability to use something due to circumstances.