What is the meaning of 當 and 自強 in 男兒當自強? 男兒當自強 is the title of the main theme in wong feihong, i was told its translation is "a man has to stand one's ground", i do not know how verbatim this translation is. 
男兒 is man, 
自強 is either "his strength" or "from strength", i am not sure about it.
As for 當, i am totally clueless what its meaning is.

What would be a verbatim translation?
Who can explain the parts in the light of grammar?
男兒 is MAN

當 is 應當， which means SHOULD，MUST

自 means 自己， SELF

強 is a verb short for 圖強，here 圖 means FIND WAYS TO DO STH，and 強 means TO BE STRONG.

So 男兒當自強 means A man should find ways to make himself strong