There is a team working on documentation. You can get in touch with them on the IRC-channel #kde-docs (see also IRC Channels) or the mailinglist kde-doc-english (see also Mailing Lists). They produce the official docs that are distributed along with the Plasma desktop as well as individual applications.
UserBase was originally intended to be a place where users could share tips and tricks. At some point we had major effort to make UB reflect the (then) current state of things, and it was maintained for some time, but unfortunately there are not many active contributors left. I would very much like to get UB back on track. Any help is greatly appreciated.