Before you start using the app, as with similar services like WhatsApp or LINE, you'll have to associate your phone number with a personal account, which should take only a few minutes. Once you've done this, you'll be able to see a list of people from your contacts who are also using WeChat.
All the conversations you have through WeChat will be saved to your device but not to the server, so only you can access them, and only from your device. No one else. This way, you can have conversations without worrying about them being saved to the cloud or on some external server.
One interesting feature in WeChat lets you talk with random users. You just have to select this mode, shake your Android device, and in just seconds you'll be connected with somebody else.
WeChat is an alternative way of communicating. You can use it to establish conversations with the speed and ease that are typical of this kind of applications. The only drawback is that its user base is smaller compared to other apps.