le 了 at the end of a sentence with a verb predicate in which an optative or modal verb occur before the main verb.

1. 
   Tā huì kāi chē le.
   他会开车了。
   Now he is able to drive a car.


This sentence implies that 'he' did not know how to drive. Compare it with the following sentence which does not have the change-of-state le 了.


2. 
   Tā huì kāi chē.
   他会开车。
   He is able to drive a car.


This sentence simply states the fact that 'he' can drive. It does not imply any change.


3. 
   Wǒ xǐhuan xué Hànzì le.
   我喜欢学汉字了。
   I have taken a liking to studying Chinese characters.


This sentence implies that 'I' did not like to study characters previously. Compare it with the following sentence which does not have the change-of-state le 了.


4. 
   Wǒ xǐhuan xué Hànzì.
   我喜欢学汉字。
   I like studying Chinese characters.


This sentence simply states the fact that 'I' like to study Chinese characters.