What are the words with " t- " ?
What are the words which are having t- like t-ugh .. when are they used?
It's to do with the gender of the words.
Feel free to take a look at https://forum.duolingo.com/comment/35345245
Also check the duolingo wikia: https://duolingo.fandom.com/wiki/Scottish_Gaelic. It nearly has all the words, and it shows when to use an, am, an t-, or a' :-)
Hope that helps. Hopefully when more tips and notes come out they will explain it :D