i live in a building apartment ,what is my house facing door? the door of the building or the door of my apartment,thank you

Both are important.
The building, how it relates to surrounding landforms, how qi enters, etc. is strongest influence.
But the apartment, how qi enters, even the hallway leading to the door, is the most immediate influence.

Plot and study appropriate charts for both. See how the building feng shui influences the apartment's

From this you can make decisions about room use, furniture placement, etc.
Cures, well I have no faith in cures....

Just wondering how do I get where is the door facing? should i get the direction when facing the door going out of our place or face the door going in?

Thanks!

For the building, the facing is the side that has open low active area (as opposed to tall, blocked less active).
For doors, the direction is the where you face when standing in the door looking out.