I wanted to ask someone about something but I don't know how to. On other wikis I have visited, writing a message is not like this. I browse this wiki on mobile. I enter a talk page and click 'Leave a Message'. A talk page opens and I write the message and post it. But it doesn't appear. A notification says that I should put 4 tilds but I don't know how to add them. Can anybody please help me?
The message you posted actually did appear so it might be an issue with your phone not displaying messages, you didn't scroll to the bottom/use the title feature to make your text easily locatable, or someone could have tried to leave a message at the same time and resulted in a conflicting edit where your post didn't go through.
As for tildes (~), those are how you sign your name at the end of your messages (four tildes).