Wechat is huge and I'm not the guy to describe it. The attractive element that people thought Elon wanted was the payment processing,
Google says:
WeChat is a free messaging and payment app that allows users to:
- Communicate: Send text messages, make voice and video calls, share photos and videos, and create groups
- Share updates: Post to a social feed called "Moments" to share photos and thoughts with friends
- Make payments: Use WeChat Pay to send money, pay bills, and shop online or in person
- Conduct business: Use WeChat to conduct business
- Translate messages: Use the localization feature to translate messages and content between 20 languages
- Call international landlines: Use WeChat Out to call international landlines at a low rate