Learn Russian: Там нет гусей. - There are no geese there.

The word нет (meaning "there is no" or "there are no") always forces the noun that follows it into the genitive case. Because we are talking about an absence of multiple geese, we need the genitive plural.

What is the dictionary form of гусей and what gender is it?

The dictionary form (nominative singular) is гусь (goose). It is a masculine noun that ends in a soft sign (-ь).

How do we get the ending -ей for гусей?

As covered in this lesson, masculine nouns ending in a soft sign (-ь) change in the genitive plural. To form it, you drop the -ь from гусь and add -ей, giving us гусей.

In English we say "There are no geese there." Which Russian word means which "there"?

The Russian word там translates to the location "there" (in that physical place). The grammatical phrase "there are no" is entirely covered by the single Russian word нет. You don't need a filler word like the first "there" in the English translation.