I see linked people (hyperlinked name) mentioned here in StackExchange but I don't understand how to do it when posting. Can anyone explain? Thanks.
It is only allowed in comments. There are a bunch of different rules behind it.
Replying in comments The owner of the post you're commenting on will always be notified of your comment. If you are replying to someone else who has previously commented on the same post, mention their username: @peter and @PeterSmith will both notify a previous commenter named “Peter Smith”.
It is generally sufficient to mention only the first name of the user whose comment you are replying to, e.g. @ben or @marc. However you may need to be more specific if three people named Ben replied in earlier comments, by adding the first character of the last name, e.g. @benm or @benc Spaces are not valid in comment reply names, so don't use @peter smith, always enter it as @peters or @petersmith.
If the user you're replying to has no natural first name and last name, simply enter enough characters of the name to make it clear who you are responding to. Three is the minimum, so if you're replying to Fantastico, enter @fan, @fant, or @fantastic.
You can use the same method to notify any editor of the post, or – if this is the case – to the ♦ moderator who closed the question.