What is the trunk version of kde 4.3 and where can i find documentation for installation.

Thanks.

Trunk is the state of development. The developers are working in trunk. If the release date comes the current source is cloned and saved in a folder (e.g. 4.3.3) (I'm not sure about this, but it shows the concept).
For general information about KDE Developing (and trunk) see
http://techbase.kde.org

For your question these links could be helpful:
http://techbase.kde.org/Getting_Started
http://techbase.kde.org/Getting_Started/Build/KDE4