What is SMS?

What is SMS? The message I received was a message from someone else or a message from you. You can say anything in the message, the more detailed the better. It is the same as voice typing combined with WeChat, so messages can be sent from your mobile phone to another person's mobile phone, or you can send one by voice, just talking to each other with frequent chat messages. What do you want to tell the other person, and then the other person will leave you a message to help you solve something, or the other person asks you for help, you can do it, you can reply to him, or you can't reply to him. It's like writing to the other person, but you can see it directly.