This page is a wiki; please feel free to contribute, and be bold with your edits!
Yes! You should find a CKAN/installed-default.ckan file under your KSP directory. This contains everything you've currently got installed. If you're using a recent CKAN release, you can also use File -> Export Installed Mods... from the GUI, allowing you to export a file to a location of your choice.
To re-install all the mods, you can use File -> Install from .ckan in the GUI, or ckan install -c installed-default.ckan from the command-line.
The CKAN checks for two things to determine if a KSP directory is "valid" or not:
- It must have a
GameDatadirectory inside it. - It must have a
readme.txtwith a KSP-likeVersionline in it.
Usually when a directory is considered invalid, it's missing the readme.txt file, or that file has been overwritten. If you're using steam, asking your client to verify your installation can help. You can also get away with replacing the readme.txt with just the following if yours is missing:
Version 1.0.2
Believe it or not, this is the most reliable way to find your KSP version number, regardless of platform or build status.
Yes! Try this one: 
If you're a human, yes. However, the CKAN can also install, manage, and upgrade your mods automatically with just a few clicks. Installing a mod, or collection of mods, becomes as easy as ticking some boxes on the client and hitting "install".
Because CKAN knows which version of KSP you're running and the dependencies of the mods you are installing, it can help you in choosing only mods that are supported for your version, leading to safer, more stable installs.
We would love to be able to detect and index new releases from Curse, but Curse does not provide an API that we can access to do so.
If you're from Curse, then please hop on our IRC channel, or open an issue, and say hi!
CKAN employ bots to regularly check for updates of the indexed mods. Sometimes this doesn't work as well or fast as one might hope. Normally you will be able to see the update within hours of it hitting the repository the bots check for info (normally Github or Kerbalstuff). Some mods are maintained via other solutions and if that is the case it might be longer before CKAN indexes the new version. If you have seen a mod go without updates for a prolonged period of time even though a new version is available please tell us.
They need to be indexed using a simple metadata file. These metadata files are hosted on the CKAN-meta repository: anyone can contribute to it to make more mods available (when possible, it's courteous to inform a mod author that you're adding it).
For mods that are distributed through a site that gives us API access, this can be as simple as writing only a few lines. See adding a mod to the CKAN for more information.
The NetKAN refers to our army of bots: they tirelessly watch out for new releases and keep the index up to date, so that you will be notified of eventual updates the next time you update your client's list.
These bots download the mod, extract any embedded metadata they find, and combine it with the release information to produce new entries in the CKAN index.
Unless you're writing metadata, you don't have to care. If you are writing metadata, then the difference is:
-
.netkanfile - Something which contains a$kreffield, and hence is not a valid CKAN document, but which can be transformed into one with the addition of external metadata. -
.ckanfile - A fully rendered document describing a specific version of a mod, which no references to external metadata required.
The netkan.exe program can "inflate" a .netkan file into a .ckan one by looking up external metadata. The advantage of us having .netkan files is that we can inflate them automatically when new releases come out, meaning you need only write them once, and we'll index new versions forever.