I was extremely confused on how to do this when I started because I do this on a mobile device. This took me a really long time to figure out too!

If you can't read the writing, "you want to get that to pop up first"

Then put an "at" sign in(if I click the actual button, it'll think I want to tag someone)

Type in the name of the person(that you want to tag) and click this. If you do it right, the name will be orange.

Again, this is for people that are on  mobile device. I don't have an actual computer, so I wouldn't know how to do it on there.