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