How can I tag people on this boards?

do you mean tag them to get their attention?

Tagging people isn't like one would find on Facebook or Twitter or other social media networks. They don't work in the threads/posts. You can tag names on your initial thread like when you tagged it:
Forums: a2k, Forumhelp

But I'm sure that's not what you actually want. The person tagged is not likely to get a notification when the thread is tagged. Only a rare few people like George get threads tagged and when they do ... it's because they requesting English to Latin translations (or similar Latin grammar and definition questions).

He must be trying to reach either me or Jespah from his previous dietary based thread.

Yes, tag them to get their attention. Like you did when you wrote @Liketoknow (blue letters), tried to do the same but the letters stayed black.

@tsarstepan. I tried to tag both of you

That's not tagging, it's replying to an individual's post. You can either reply to the topic, which is what you've done, or you can click on the reply box over the individual's relevant post, which is what I've just done.

Thanks a lot!

That was just a text link (an active link to refer back to the destination post of the link). It just means it's clickable. Sadly, one can't get notified if you use it to try and tag people. A useful feature not found here (yet?) at a2k.

You've got it.

the only way to get someone's attention is to send them a PM, but they have to be logged in to see the notification...

Thank you so much. Another question: How can I quote?

go to your preferences https://able2know.org/account/preferences/

in the Topic Preferences section, make sure "Show quote button" is set to Yes

Thanks

Tag . . . you're it . . .