Learn Hardcore Arabic (Egyptian): قابلته عند باب العمارة امبارح. - I met him at the building door yesterday.

A useful thing to notice: in Egyptian Arabic, the attached pronoun ـه is often pronounced more like -o or -u in everyday speech, so learners may hear something like ʔābalto.

Why is there no separate word for I in the sentence?

Because the verb already shows the subject.

In قابلت the ending -ت tells you the subject is I in the past tense. So أنا is not necessary.

You could say أنا قابلته عند باب العمارة امبارح if you want emphasis, but native speakers usually leave أنا out unless they need contrast or emphasis.

What does عند mean here?

Here عند means at, by, or near.

So عند باب العمارة means something like:

at the building door
by the entrance of the building
near the building entrance

In other contexts, عند can also mean have when used with a pronoun, like عندي = . But in this sentence it is just a location word.