Sie hat einen Elefanten.
Duolingo translated the above phrase as "She has an elephant." Is "Elefanten" both singular and plural for elephant?
There are some words called "weak nouns" which are the same in plural and singular in some cases. I think this is not interesting for beginners but if you want to learn about it, search google for "weak nouns" or "n-declination". You could also see here: http://www.vistawide.com/german/grammar/german_nouns03.htm
There is a group of nouns in German that end with -n or -en in plural, that also get these declensions in all other cases except nominative. They also don't get an umlaut. The nouns in this group are all masculine (der) and describe some animals, nationality and people.
Examples are "Der Elefant", "der Schwede" and "der Student", respectively. So e.g. elephant would be: (nominative) der Elefant, (accusative) den Elefanten, (dative) dem Elefanten, (genitive) des Elefanten. Those are all singular, and in plural it is: die Elefanten.
Pretty much you just have to learn by heart which words behave like this, but they are relatively few.
"Elefant" is the nominative case. Here you need the accusative case, which is "elefanten".
In sentences where there is only one object the object is often in the accusative case. Common verbs in such sentences are: haben, sehen, hören, and finden. Movement is not necessary for the accusative case.