...that you do not need to erase a CDRW before rewriting it manually since K3b can do that automatically before writing.
...that you do not need to bother with any settings if you do not know what they mean. K3b is able to choose the settings best suited for you.
...that K3b has two types of settings. On the one hand K3b has settings like most TDE applications have accessable through the configuration dialog via the settings menu; on the other hand every K3b action dialog has three buttons to load and save defaults for that action. This way one may, for example, set the defaults for CD Copy: these defaults will then be loaded every time the CD Copy dialog is opened. The button K3b defaults will restore the factory settings in case you do not know if the settings you chose are appropriate.
...that you do not need to bother changing the settings marked as advanced if you do not know what they mean. K3b's defaults are suitable for most daily use.
Just left-click one of your devices in the device and file tree and see what happens. K3b opens a specific window based on the media's contents. For an audio CD for example you will be given a list of the tracks with the possibility to rip these tracks to any format supported by K3b (like mp3 or Ogg-Vorbis).
...that K3b lets you choose media instead of devices for burning. So if you want to burn to a certain medium simply insert it and wait for K3b to detect it. It will then appear as your burning medium.