-How do you enter a building?
Since you're still confused, I'll try to help you out. I don't know where this was answered for you though, so I'll cover everything.
Well, first, draw your screen. Add your building or cave or whatever you want to be the place Link enters, and add a tile warp tile (on the default tile set, the tile should be black and a several rows down. If my memory is right, its tile 47). It should be called "Cave Walk Down" or something like that. There are also other tile warp combos that you can use.
Then go to Data, and tile warp. Enter in the screen where you want Link to be warped to (screen 80 if it's a special item room or something like that). Make sure you set up the DMap, also, because I don't think it will work if the DMap isn't set up.
When you play the quest, walking into the tile warp will take you to your destination. Don't forget to place the blue square in front of the building (press page down and click on the blue square to place it). This is the position Link will be when he exits the building.
-Edit the building?
To edit the building, just edit the screen that Link is being warped to (see above). You can also edit screen 80 to look like a house, if you wish.
-Enter a dungeon?
Do the same as said above. The only different thing is you need to enter the Relative coordinates, not the absolute coordinates. The relative coordinates are the coordinates used on the DMap, and the absolute coordinates are the coordinates used in the map at the bottem-left corner of the main screen. I guess that's the best I can explain it. Look at AlphaDawg's tutorial to learn more about this.
Also, don't forget to set up the Dmap (see below for dungeon Dmaps).
-Edit the dungeon?
To edit the dungeon, make a new map. Then make a new Dmap. Set the Dmap type to "dungeon" and the Level to "1". The first 8 levels correspond to the triforce piece in the dungeon. Level 9 has the same properties as the others but there is no triforce piece. Levels 10-infinity are dungeons with no triforce pieces.
First, you need to make a basic dungeon room. I believe there's a sample room in Zquest to use. Now copy/paste that room into how you want your dungeon to look. Then go into the Dmap for this dungeon and center the dungeon so all of it appears on the left map. Then take the coordinates from the left map and map out your dungeon on the right by pressing the squares. What you put on the right is what your dungeon map will look like when Link picks up the map. Make sure the coordinates on the left are the same as on the right or else your dungeon might not match up with the map.
-Place people?
Just make people tiles and place them on the screen. You can't talk to people like this, though. One method to make it so that you can talk to people outside of interior places is this (in theory, never tried it myself): make the person a tile warp so when you walk into the person you can be warped to a place that looks exactly like the place before you were warped and then have him talk there.
I hope I helped "unconfused" you. I'm not to good at putting helpful thoughts into words, so sorry if it sounds weird. I'm sort of a newbie too, but I hope I helped 😃