Here's a breakdown:
* അത് (athu) - it
* ശരിയാണ് (shariyanu) - is true
You can also say:
* സത്യമാണ് (satyamanu) - it is true (literally, "it is truth")
* തെറ്റല്ല (thetallu) - it is not false (literally, "it is not wrong")
The choice between these depends on the context and the level of formality you need.