In one sentence, describe what the following article is about:

It's a green app that contains a white phone icon inside a white text bubble. It's an icon of overlapping text bubbles at the bottom of the screen. Select the chat with the attachment you wish to download. Select the attachment you wish to download. It's the square containing an upward-pointing arrow in the lower-left corner of the screen. The attachment has been saved to your iOS device.

Summary:
Open the WhatsApp app. Tap Chats. Tap a chat. Tap an attachment. Tap the "Share" icon. Tap Save.