The Doors of the CharLoft are a subject unto themselves - these netherworldly connections seem to link to countless places, times, and dimensions - often many different ones in the space of a minute. The functioning of a Door is usually quite simple:
1) The person in the alternate location opens a door that has been linked to the CharLoft doors while thinking about going there. (Or sometimes, just on accident; that's how many people wind up there in the first place.)
2) When opened, the door seems to transform subtly to match up with the door that opens inside the CharLoft, whether this be the front door or any other door in the building. Occasionally, doors literally appear within the CharLoft just long enough to disgorge an incoming traveler before ceasing to exist behind them (typically when all other Doors are already open and someone is attempting to enter - particularly the front Door.)
3) When someone wants to return to their own home location, they merely think of 'home' - whatever that may be for them - and open the door. Strong visualization is key, and having a Door that already has linked to that location before is very helpful. Attempting to go to locations (different worlds, different places, or different times) one is less familiar with is perfectly possible, though not necessarily successful.
4) On rare occasions - or if the Owner has developed a strong dislike for the person in question - a Door may cease to function for a particular individual, or worse, open onto a distinctly hostile or inaccurate world. A person might not know the difference until they turn to the Door that brought them there and discover that it has been locked behind them, or is no longer there. This seems to happen with greater frequency if the Owner dislikes the customer, but even being on excellent terms with him and the staff is no guarantee that something won't go wrong…
5) Those who have studied the Doors carefully have noted that there is a contractual obligation inherent in the Door similar to those used in demonic summoning rituals, limiting the amount of harm the user can bring to natives of World's End and related pocket dimensions such as the Char Loft. Thus, innate powers that would normally threaten all life within miles are reduced to perhaps a few feet of misfortune, and the ability to generate enough heat to boil away atmospheres is reduced to being able to sizzle things or very gradually build up enough heat to melt metals. Other, more direct applications have been witnessed, particularly if a person is actively engaged in combat through the Door (a nuclear explosion has been blocked from passing through the Door, as have several world-grade apocalypses). Those relying on this effect as a handy shield, however, may be setting themselves up for an unpleasant disappointment.
6) Doors can be locked so that certain people cannot access or make use of them, or even severed entirely so that an unpleasant dimension is permanently banned from entry. Likewise, some dimensions that no longer exist cannot be accessed (once it's confirmed that a particular Door destination leads to the Void, future attempts are likely to be blocked for the safety of inhabitants.) Notably, Doors that are otherwise mundane in nature can be locked and barred in the usual ways; people who dislike having interdimensional wanderers keep popping out of their dresser may choose to put a lock on the outside, for example. However, the opening of a dimensional Door tends to override any frame-based lock, so bars, deadbolts, chains, and similar restrictions are advised. This also does not necessarily prevent a Door from opening in thin air without a frame!
7) Doors tend to work most readily when not observed. Whether because the original creator had a penchant for quantum particle physics or because it just makes the magic easier, the easiest way to find a Door is to enter one with a strong desire to be somewhere else in particular and without looking where one is going, particularly if that desire is 'anywhere but here'. This seems to be how most people first discover the Char Loft in particular, and how people best use the Doors to find new places to explore.
Establishing a contact with the Doors from a new location generally requires familiarity with the CharLoft and its Doors, and either an innate talent for manipulating spacetime, or being within the CharLoft and attempting to will a connection into existence by trying a Door. The latter is far less difficult to attempt, but is far more likely to result in inaccurate openings, at least for the first few tries.