double le , the first 了，<font style="font-size: 16px">pronounce </font><font style="font-size: 16px">liao, </font><font style="font-size: 16px">an other one pronounce </font><font style="font-size: 16px">le , </font><font style="font-size: 16px"> so we say</font><font style="font-size: 16px"> liaole , ,</font><font style="font-size: 16px">its correct ,  it has two meaning ,  if  ppl ask u "do u understand ?", u say</font><font style="font-size: 16px"> liaole,</font><font style="font-size: 16px">here its mean "understand" , if ppl ask u "how things going ?" u answer liaole, here is an other meaning ,mean u worked out ,    </font><font style="font-size: 16px"> i hope it can help u.dont mind my bad english ...</font>

most of time  we  use 了in the end of sentence ,its mean past tense , like "i finished",u can say“wo hao le ” （"我好了），"or " wo wan cheng le "我完成了)  ， some ppl ask u "你吃晚饭了吗？”(did u have dinner?) ,then u answer "我吃了",( "yes ,i did " ,)    
 
i try to make it clearly ok? ... if 了 after a verb,   mean past tense , this   action u finished already .such as "我完成了”（i finished ），but.... if u say "我快完成了"，its mean "i almost  finished ",or "im going to finished "   so ,if there is a "快"before了 ,its mean "im going to .." 
 
if 了after a  adj or noun, then its mean “enough ” ,like "qingchu le ma ?"(清楚了吗？) mean "clear enough ?” ,“gou le ？”(够了？)，mean“enough?”

i tried my best ,.cuz chinese is really hard to explain   , u could write some sentences ,i can  correct that  

Many many Thx for your clear answer. (don't worry: your english is way much better than mine).
And when should i use liao alone? is liao written in the same way of le (了)?
It's beacuse i saw somewhere ppl using liao at the end of some sentence. (i mean saw that written in Pinyin).