How to do all this stuff is in the help that comes with KDevelop. Look at the "Working with Source code" section, then "Writing Source Code".
To create an implementation of a function type out the function like it's a declaration, but do the braces. Then select the function name, then Code Menu -> move to source, or Ctrl+Alt+S. It doesn't work if you put the semicolon in as per a declaration.
Hope all goes well.
EDIT:
I recently tried Code::Blocks, and am leaning towards it being better than KDevelop. I really like it's class wizard.
Speaking of intellisense: http://i.imgur.com/2AWTqcV.png
The plugin that allowed this is no longer being updated, and I don't know if it was ported to linux or not (it used a clang.dll file, so...)
Hang on, the Linux IDE's have the same thing don't they? I have KDevelop, Code::Blocks, Eclipse & QtCreator - they all do code completion rather well IMO. I haven't used VS, so I can't compare in that direction, but for what I have I couldn't ask for any more functionality.
Just wondering what you think is missing? Bear in mind you need to have the relevant files included for code completion to work properly, but I thought that would be a requirement no matter which IDE you use.
@L B
I have a vague idea that some the Linux IDE's can be made to work with clang, no idea about stand alone C++ aware editors though.
Ok, one good thing abut KDev is that it is a mature application, so it might do some things well that the others don't. Also KDev is good for compiling all kinds of Langauges & scripting, which the others don't do at all - or at least not to the same extent.
But in terms of code completion, it seems they all do that these days.