Because Italian often leaves out subject pronouns when they are clear from the verb form.
So:
The tu is understood from guarda. This is very normal in Italian.
In many situations, là and lì both mean there, and native speakers often use them almost interchangeably.
A rough tendency is:
But this is not a strict rule in everyday speech. In a sentence like this, both could work:
Both are natural.
Because vicino normally takes the preposition a before a noun:
Then a + la becomes alla:
So vicino alla porta literally works like near to the door.
In standard Italian, vicino la porta is generally not the preferred form.
Here vicino is functioning in a prepositional/adverbial way, meaning near.
In Italian, vicino can be used in different ways:
So in this sentence, it is part of the location phrase that tells you where to look.
The comma is not absolutely required, but it is very natural.
It shows a small pause between:
It helps the sentence sound like spoken guidance: first pointing, then specifying the place.
Without the comma, the sentence can still be understood:
But the comma makes the structure clearer on the page.
Yes, you could, and it would still be natural.
Adding là makes the pointing feel a little more immediate or visible, as if you are indicating a spot with your eyes, hand, or finger.
So là is not strictly necessary, but it adds a stronger sense of there.