Solomon

There are three types of damage in Intersect right now (hopefully we'll see some sort of editor for this so we can increase the damage types allowing attribute based damage i.e. wind/fire/water/dark/light in the future, whether official or through a source tutorial.)
Physical damage can be blocked by the player's equipment and endurance.
Magic damage can be blocked by the player's equipment, endurance and possibly (though also may not be) intelligence/wisdom.
True damage is applied regardless of level/stats/gear. So a level 1 slime that hits 5 will always hit 5 using true damage, but a level 1 slime that hits 5 against a level 1 player using physical damage, will hit less against a higher level payer.
 

Firstly to answer your question, you place an event tile on the tile where the door is, you make it impassable then set the condition to be Player Use (I think) then you set a global variable (if you want other players t see the door animating, if you don' then use a player variable so only that player can see it) to have the door open/closed and you change the door animation depending on the variable.
 
Secondly to add my opinion, after playing Arcwyre, it's a nice idea but it just slows the player down from going inside a building (it's doubly frustrating if you accidentally leave a building as you now have to wait the 1-2 seconds for the door to open.) I would recommend that instead of having it done on player interaction (which just adds a frustrating and inconvenient 'feature' for the player) you should have the tile automatically open the door when a player steps on the tile. I personally would rather doors open when I walk past the shop than have to open every single door to get inside a building, one is an inconsequential thought of "oh that's weird, I wasn't even going inside, lol" and the other is a negative thought of "that's really annoying."