just started

Definitely use the second tutorial above, not the firs t- the first is very outdated now and half of what it says is no longer correct. It says so at the top of the tutorial, so hopefully no one will make the mistake of using it should they stumble upon in it.

Sounds like the problem here might be more basic, though, if he can't get chords to appear at all. The process should be very simple. Click (single, not double) a note, press Ctrl-K, and a cursor should appear above the note where you can start typing. You do have to type chords that are recognized by MuseScore, and the details of that are things covered in the tutorial and the handbook. But even if you type absolutely garbage, it will still display - it will just display poorly, and the transposition won't work, and other bad things happen.

Not sure what plugin you mean. No plugin is required to create chord symbols. It's literally as easy I described above:

1. Cick a note (single click, not double click) - the note should turn blue
2. Press Ctrl-K to enter chord symbol entry mode - a flashing cursor sholud appear above the staff
3. Type your chord symbol - it should appear as you type
4. Hit Space to move to the next beat or note to enter another chord, or hit aesc to exit chord symbol entry mode

So, are you following these steps? If so, what *exactly* goes wrong? Does the cursor not appear when you press Ctrl-K? Does your symbols not appear as you type? Does it turn into garbage when you hit Space or Esc? Can you post the score you are having provlems with and list *exactly* what you are doing and what goes wrong for you?

Perhaps the problem is simpler still - if you are on a Mac, you have to mentally change "Ctrl" to "Cmd" in all instructions for all computer software that also runs on Windows or Linux. So instead of Ctrl-K to enter chord mode, you would need to press Cmd-K. And similarly for just every keyboard shortcut you ever read about for any program that also runs on Windows or Linux.