Most KDE software uses CMake as a buildsystem. This page is the starting point for CMake-related documentation for KDE software.
You should be aware that there are two main development platforms that KDE software is based on: the older kdelibs4, and its replacement, the KDE Frameworks. Quite a bit of KDE software is in the process of transitioning from kdelibs4 to KDE Frameworks, and the way CMake is used is slightly different between the two.
This page contains some tutorials to help you get started on building a CMake-based buildsystem. This is the recommended way of building your software if you use KDE technologies, such as KDE Frameworks.
If you just want to build a CMake-based project on a UNIX system, the following recipe will do that:
cd /path/to/project/source
mkdir build
cd build
cmake -DCMAKE_INSTALL_PREFIX=/where/to/install/to ..
make
make install
Don't forget to replace both paths. If you want an explanation of what this command does and how to make CMake behave differently, or you want to build on Windows or OS/X, see the building with CMake chapter.
You may want to check out the CMake wiki, although beware that it contains quite a bit of out-of-date information.
See https://techbase.kde.org/ECM5/IncompatibleChangesKDELibs4ToECM.