Learn Dutch: De bus stopt bij de bushalte. - The bus stops at the bus stop.

In Dutch, bij is the standard preposition for being at a specific station, stop, or general location. You say bij de bushalte because you are physically waiting near or by the sign or shelter.

Where would I put the word al to say 'The bus is already stopping at the bus stop'?

You would place it right after the verb, making it De bus stopt al bij de bushalte. In a simple main clause like this, time particles like al typically go directly after the conjugated verb.

How would the meaning change if I used the time particle pas right after the verb instead?

If you say De bus stopt pas bij de bushalte, you are using pas to mean 'not until' or 'only'. It implies the bus skipped earlier stops and this is the very first place it is stopping, or that it is only arriving just now.

How do I express that the bus is 'still' stopping at the bus stop?

You use the particle nog. The sentence becomes De bus stopt nog bij de bushalte. Just like al and pas, it sits right after the verb to show that the action is currently ongoing.