kernel – How to recompile coreutils?

I am trying to recompile coreutils for my ubuntu 20.04 I cloned the repository from git:// and followed the README-hacking, all passes without error but my change to the source code does not appear in the terminal, also tried reboot but no luck. I had also tried to delete the binary from /bin/ and /usr/bin/ and reboot, weirdly I am still able to use the command!

My question is:

What am I missing to recompile and install the coreutil?
Why I still able to run core command even I deleted the binary?
makefile from coreutil does not build the binary to /bin or /usr/bin, where does it build to?