Three ways of learning the meanings of words that begin with an apostrophe (until the bug preventing them from displaying their hints is fixed):
1 - In the first few lesson units, the most important words that start with an apostrophe are translated. This includes 'IH for the "Dialogue" unit that this sentence belongs to.
Please always read the tips and notes before you start a new unit.
The tips and notes are not available to most users of mobile apps, which is one reason why I personally would discourage users from using the app to learn Klingon (though they may be useful to practise what has been learned through the Duolingo website).
In the Duolingo website, https://www.duolingo.com/ , you can see the tips and notes for a unit by clicking on the lightbulb icon after selecting a unit:
2 - Guess at the meaning, then learn from the correction that the system gives you. In this case, you can probably guess that 'IH is a verb because it has a noun torgh after it, presumably the subject, so you might guess "Torg icks" or "Torg is icky". Then you will be corrected and will learn that it actually means "Torg is handsome".
(One disadvantage: the system tries to show you a correction that it considers close to what you wrote, but its idea of "close" is not always a human's idea of "close", so it might show you an alternative that is considered acceptable but is not the best possible translation.)
3 - look up the meaning in a dictionary, such as the two that E.T.Gregor and kahless62003 pointed you at, or in the printed book The Klingon Dictionary, which is a good idea for any serious student of Klingon to have anyway. (Despite its name, it's not just a dictionary but also an introduction to the language and its grammar.)