اليوم أشتري تذكرة القطار، ثم أنتظر في المحطة.

Today I buy a train ticket, then I wait at the station.

Breakdown of اليوم أشتري تذكرة القطار، ثم أنتظر في المحطة.

• اليوم: today
• في: at/in
• المحطة: station
• القطار: train

Questions & Answers about اليوم أشتري تذكرة القطار، ثم أنتظر في المحطة.

Why does the sentence start with اليوم? Is that normal word order in Arabic?

Yes. Putting a time word like اليوم (today) at the beginning is very common in Arabic to “set the scene.” It’s a fronted adverb of time.
A more neutral order is also possible, e.g. أشتري اليوم تذكرة القطار، ثم أنتظر في المحطة. Both are correct; starting with اليوم adds emphasis on when.

Why is أشتري spelled with an initial أ? What does it mean grammatically?

أشتري is the present tense (imperfect) verb meaning I buy / I’m buying. The أ- prefix marks 1st person singular (I) in the present tense in Modern Standard Arabic.
Root: ش ر ي (to buy). Form: يشتري = he buys, أشتري = I buy.

Does أشتري mean “I buy” or “I am buying”? Which one should I understand?

In MSA, the present tense can cover both simple present and present continuous, depending on context.
So اليوم أشتري... naturally reads as Today I’m buying... (a current/near-future action), but it can also be translated as Today I buy... in a more general sense. Context decides.

Why is it تذكرة القطار and not something like “the ticket of the train” with a separate word for “of”?