Giulia is spot on with those directions.
If you post a comment on something and then hover over a username (not available on mobile or tablets) and you get the profile hovercard to pop up and it is mostly blank you may have to refresh the page and hover again to see the message button. I am finding that right after you reply to something or otherwise post on the site that not all the information loads on a hovercard until after refresh/reload the page.
Otherwise going to the profile works as well. If on a mobile device (phone or tablet) flip your device on the side to see more options. Change to Desktop mode in your browser if you feel it's showing you a simplified view of the site.
Additionally, if you know the person's username you can also click the Pencil icon (available on any page) and then choose Message from drop down to start a private message.
Private messages are fun and I definitely recommend them for things that are sensitive however I do recommend that most things are posted publicly for the benefit of all. 
Mark
EX Community Manager
Trisha76 You can also go to user profiles and there is an option for Messaging as seen in the red box.
On a Computer there is an option if you hover over a username, then a pop-up will appear like below with option to message but this won't appear on mobile.
As for what else you can do on a 10 year old iPad. You probably can add some emojis to posts but the keyboard has updated in the last 10 years so that may be limited.
Trisha76 wrote:
I finally found this today! I’m not sure I got everything on the top paragraphs but I am going to try the pencil for private messages that sounds good. I still have so much to learn and I really do think using my iPad keeps me from adding all those cute features that I want to add to my comments but I am unsure.
