Learn Farsi: رانندگان امروز خیلی خسته هستند.

The singular word for driver is rānandeh (راننده). It ends in a silent 'h' (ه) which makes a short 'e' sound. When adding the animate plural marker to a word ending in this silent 'h', Farsi replaces that letter with a 'g' sound to smoothly connect the word parts, making the ending -gān (گان).

If we used the regular plural marker -hā (ها), would the sentence still mean the same thing?

Yes! You could absolutely say rānandeh-hā (راننده ها) here. The marker -hā is the standard everyday plural for everything. The -ān marker (and its variations like -gān) is a bit more formal and is reserved almost entirely for living things like people, but both mean the exact same thing.

Why is the time word emruz (today) placed right after the subject instead of at the end of the sentence?

In Farsi, time words almost never go at the end of the sentence. They usually go at the very beginning, or right after the subject like we see in this sentence. Saying emruz rānandegān... would also be completely natural and correct.

Why do we have to use the plural verb hastand (هستند) here?

Because the subject, rānandegān (drivers), refers to people. In Farsi, when the plural subject is animate (human or animal), the verb must match it and be plural. If the plural subject were an inanimate object, like a group of cars, the verb would often just be singular!