"The son has a son."
Translation:Der Sohn hat einen Sohn.
Dec 11, 2015 - Anirudhmkonduru, perhaps you could start at the beginning of a German grammar site, review what you know and fill in the missing bits. These sites have free overviews of German with lots of detailed discussion. Then you will feel a lot less frustrated and overwhelmed. Coupled with Duo, you will be happier with your progress.
Those are my favorite sites, maybe others have further suggestions.
Oh! And here is a review of the cases in English, so it will make more sense when you are looking at German grammar.
October 6, 2015 - Here are the basic parts of speech for English: http://grammar.about.com/od/basicsentencegrammar/a/POS.htm
If you become a little more familiar with English grammar, then the discussion of German grammar will make more sense. It won't take much, just knowing the parts of speech will take you a long way.
German uses endings to indicate which parts of speech the words are playing in the sentences. A basic noun can be the subject (nominative), direct object (accusative), an indirect object (dative), or a possessive (genitive). That's an extremely simplified overview. Like learning the rules of a game, it takes a while to get all the details.
Here are some basic German grammar sites for English speakers:
Einen is accusative case. The first son had the second son. The second son did not do anything in this sentence. The first son only did something to him (having him). Therefore, it is accusative case. It's the same as the difference between I and me. Note that einen is not used for neuter nouns, in that case it's just ein.