Quando arrivi, suona il citofono e aspetta davanti al portone.

Because Italian often omits subject pronouns when they are clear from the verb form or the context.

Here, the sentence is clearly speaking to one person:

• arrivi
• suona
• aspetta

So Italian does not need to say tu. You could add tu for emphasis, but normally it is left out.

Italian often uses the present tense to talk about a future action when the timing is already clear, especially in instructions like this.

So Quando arrivi means when you arrive.

Using quando arriverai is also possible in some contexts, but quando arrivi sounds very natural here and makes the instruction feel direct and immediate.

English does something similar:

• When you arrive, ring the intercom not
• When you will arrive, ring the intercom

Here it is a command.

The form suona can mean either:

• he/she rings or
• ring! when speaking to tu

The context tells you which one it is. Since the sentence is giving instructions, suona means ring!

The same is true of aspetta:

• it can mean he/she waits or
• wait!

Here it clearly means wait!

They are the imperative forms for tu of -are verbs.

For tu, the imperative of most -are verbs ends in -a:

• suonare → suona
• aspettare → aspetta

This is why the commands look like that.

For comparison:

• Lei formal: suoni, aspetti
• voi plural: suonate, aspettate

If you speak to one person formally (Lei), you would say:

Quando arriva, suoni il citofono e aspetti davanti al portone.

If you speak to more than one person (voi), you would say:

Quando arrivate, suonate il citofono e aspettate davanti al portone.

So the original sentence is specifically addressed to one person informally.

Citofono is the intercom system at the entrance of a building, the thing you use to buzz an apartment and often speak through.

It is not just any bell. A useful comparison is:

• campanello = doorbell / bell
• citofono = intercom / buzzer system

In everyday Italian, suonare il citofono means to ring the intercom/buzzer.

Porta means door in general.

Portone usually means a large main entrance door, especially the big front door of an apartment building or courtyard entrance.

So in this sentence, davanti al portone means waiting outside the building’s main entrance, not outside the apartment door itself.

Because davanti normally uses the preposition a in this meaning:

• davanti a = in front of

So:

• davanti a + il portone becomes
• davanti al portone

This is just the normal contraction:

• a + il = al

More examples:

• davanti alla casa
• davanti al negozio
• davanti ai ragazzi

Because Quando arrivi is an introductory time clause, and it is separated from the main instruction with a comma.

Structure:

• Quando arrivi, = time clause
• suona il citofono e aspetta davanti al portone. = main clause

This works very much like English:

• When you arrive, ring the intercom and wait outside the main door.

The comma is standard and helps readability.

Yes, it is very natural.

In Italian, suonare can take things like campanello or citofono directly:

• suona il campanello
• suona il citofono

So even though English often says ring the bell or buzz the intercom, Italian uses suonare very naturally here.

You can, but it usually sounds unnecessary unless you want emphasis or contrast.

Normally, Italian prefers:

• Quando arrivi...

If you say:

• Quando tu arrivi...

it may sound like you are stressing you, as in:

• When you arrive (not someone else)

So in ordinary instructions, leaving out tu is the most natural choice.

Because both actions belong to the same situation.

The meaning is:

• When you arrive, ring the intercom
• and wait in front of the main door

Italian does not need to repeat quando before the second verb, because it is understood that both commands happen after arrival.

This is very natural and economical in Italian, just as in English.