It means someone doesn't have that much moral or abilities. Usually it's way of being modest in China, not common in western countries maybe. E.G. --你将成为我们的领袖。（You'll be our leader.） --我何德何能来担此重任呢？（How can I? I am not that capable or noble.）

德 = virtues, good qualities 能 = ability The phrase "何德何能" is used in a rhetorical question, such as "他何德何能出任我们组长?" The meaning is "He does not." Thus it is often used in a criticism or a challenge.

德：morality 能：capacity 何：which / which kind of In ancient china, if a person want to be a leader, such as a mayor, a king, he must have two things: 德 and 能. Furthermore, 德 is more important than 能, meaning that a leader could have no 能 but he must have 德. This is why we put 德 first ---- because it is more important. 何德何能：which kind of 德 and which kind of 能. When we select a person to be a leader, normally he should be modest. For example, we are a team, and I say that you can be our leader, then you can say: no, I am not good enough ---- now you are modest. In chinese, we say: 我有什么样的品德和什么样的能力，去担任这个职位呢？ ------- meaning that I am not good enough, I can't be the leader. For this case, we have a 成语：何德何能 to express the same thing. e.g. - "plz be our leader." - "我何德何能，做大家的领导呢？"