Geese is the plural form of goose: one goose, two or more geese. Yes, I know, it should either be gooses or we should also say meese, cabeese and he leese the screws, but English is one of the most messed up and therefore most widely spoken languages ever
How do you know if it is saying eats or eating. I get it wrong all the time.
Generally, the present continuous ("eating") would be used to describe something that is happening right now.
So "the bear is eating a goose" (right at this moment, the bear is in the process of eating a goose).
On the other hand, the simple present ("eats") would be used more to describe a HABITUAL action.
Thus, "The bear eats a goose every Christmas" (this is a habitual action that the bear repeats at a certain time - OK, I'm entering into the Duolingo spirit of silly sentences here, but hopefully it's a clear enough illustration).
Or let's suppose the bear is a glutton and more than one goose is involved:
The bear is eating geese (right now, the bear is in the process of eating geese).
The bear eats geese (geese are part of the bear's regular diet - it's probably not eating geese right at this moment though).
Other languages like Spanish make this sort of distinction between simple and continuous present, but Dutch is one that doesn't. So you have to look at the context and basically ask yourself whether the sentence appears to be describing something happening right now (in the process of occurring) or whether it's talking about something more habitual. Sometimes it can be ambiguous though (but I think when it's ambiguous, Duolingo will usually accept both "eats" and "eating" or whatever the relevant verb is).
Hope this is of some assistance.