Replying to posts, and mentioning people

Hi, I hope that this is the right section of the forum to post. The subject pretty much says it. I am wondering if there is a way to reply directly to post that people post on a website. For example, if I’m following a topic, and I want to reply directly to a comment, the only thing I know to do is type in RE: and then the name of the subject to which I’m replying. Is there an easier way? Also, if needed, how do I mention users directly. I’ve seen this happen before in the website, where it will link to users and posts. Hope this makes sense. Please let me know. Thanks