如果你想表达你需要某个物品，你可以这样说：

"I need a (item)."

例如：

"I need a pen."
"I need a new pair of shoes."
"I need a bottle of water."

如果你想在询问别人是否有某个物品时，你可以这样说：

"Do you have a (item)?"

例如：

"Do you have a pen?"
"Do you have a new pair of shoes?"
"Do you have a bottle of water?"

希望这些信息能帮到你！