Learn French: Pardon, où est la gare ? - Excuse me, where is the train station?

The accent changes the meaning of the word! Où with the accent means "where". Without the accent, ou means "or". They sound exactly the same when spoken, so the accent is just there to help you tell them apart in writing.

Is it okay to say la gare est où instead?

Yes! In everyday spoken French, it is very common to keep the normal sentence order and just put the question word at the end: la gare est où ? (literally "the station is where?"). The order in this sentence (où est la gare ?) is standard and great for both speaking and writing.

Could I use excusez-moi instead of pardon?

Absolutely. Both are great ways to get someone's attention politely on the street. Pardon is slightly shorter, but using either one before asking a stranger for directions is polite and highly recommended in France.

How do I know to use la instead of le before gare?

Gare (train station) is a feminine word in French, so it takes the feminine word for "the", which is la. Because you usually cannot guess a word's gender just by looking at it, it is a great habit to memorize the la or le together with the noun when you learn new places.