Learn Polish: To jest kot.

Polish doesn't have articles like "a", "an", or "the". The word kot alone can mean "a cat" or "the cat" depending on the context. Here, "This is a cat" is the most natural English translation.

Does the word to change since kot is a masculine noun?

No, it doesn't! When you use the phrase To jest... (This is... / It is...) to introduce or point something out, the word to is fixed. You will use to regardless of whether the noun following it is masculine, feminine, or neuter.

What grammatical case is kot in here?

It is in the Nominative case, which is the basic "dictionary form" of a noun. When you introduce something using To jest, the noun that follows always takes this basic Nominative form.

Could To jest kot also mean "It is a cat"?

Yes! The Polish word to is very flexible. Depending on the situation, To jest kot can be translated as "This is a cat", "That is a cat", or simply "It is a cat".