[decondelite]

Mike, smit explained everything with his 2 links. Entering a house means:
1) Changing the player's position with SetPlayerPos
2) Changing the player's interior with SetPlayerInterior
3) Changing the player's virtual world with SetPlayerVirtualWorld
The same goes when you exit the house: you set the player's position to the ones in front of the door, set the interior to 0 and the virtual world to 0.

But he forgot to give you another useful link:
https://sampwiki.blast.hk/wiki/InteriorIDs