Help:Introduction to talk pages/User talk pages
Everyone contributing to Wikipedia has their own user talk page. On this page, anyone can leave a message for you. People can ask you questions or give you advice. There are some automated 'bots' that may also add helpful messages.
Unregistered users on a shared internet connection, like school or home networks, get a shared talk page. If someone leaves an unregistered user a message, the user will see a note saying "You have new messages", which will be visible at the top of whichever page they are looking at. It looks like this:
In either case, viewing the new message will remove the notification. To reply, you can put a comment below the message on your user talk page (although the other person won't automatically be notified if you reply this way), or you can go to the user talk page of the person you are replying to.
Generally, you can find an editor's user talk page by following the link labelled "talk" in their signature, located at the end of their messages. You can always reach their user talk page by clicking on their name in the signature, and then clicking on the "Talk" tab, as you would with an article.