Learn Polish: W nowej pracy jest dużo stresu. - There is a lot of stress in the new job.

Because of the word dużo (a lot). In Polish, quantifiers like dużo, mało (a little), and trochę (some) force the following noun to take the Genitive case. Stres is a regular masculine noun, so it takes the ending -u to become stresu.

How does this sentence translate to 'there is' when there's no word for 'there'?

Polish doesn't use a filler word like 'there' to state that something exists. You just use the verb jest (is). So, jest dużo stresu literally translates to 'is a lot of stress', which naturally means 'there is a lot of stress' in English.

Why is it nowej pracy instead of nowa praca?

This is a quick refresher on the Locative case! The preposition w (in) requires the Locative case when describing a location. Since praca (work/job) is a feminine noun, the adjective nowa changes to nowej, and the noun praca changes to pracy.

Can I change the word order and put w nowej pracy at the end of the sentence?

Yes, you can! Jest dużo stresu w nowej pracy is also completely correct. Polish word order is very flexible. Starting with w nowej pracy just puts a little more emphasis on the fact that this happens at the new job, rather than focusing purely on the stress.