I want to install xctool for for understanding and practice but I'm not sure whether installing it completely replaces the xcodebulid or it will be a separate installation and will not affect my normal build from Xcode(play button)
xctool will not replace xcodebuild, contrary to what they state on their Github page. It is just built on top of xcodebuild, so you don't have to worry about loosing your xcodebuild when you install it. In fact, xctool would not work if the command line tools are not installed on the system.
If you consider using xctool for building, you may want to reconsider your choice. This is what they say in the docs:
Note: Support for building projects with xctool is deprecated and will not be updated to support future versions of Xcode. We suggest moving to xcodebuild (with xcpretty) for simple needs, or xcbuild for more involved requirements. xctool will continue to support testing