"I can understand the book."
Translation:Táim in ann an leabhar a thuiscint.
While Is féidir liom is used, I wouldn't consider it better, as such. is féidir emphasises the fact that it is possible for me to understand the book, in ann and ábalta emphasis that I have the capability. In many cases it doesn't matter which phrase you use, in some cases, it might be more appropriate to use one rather than another.