Each sub system is a snapshot of parent system. That is, if you create a "bin" directory in your home dir, the system(most linux distributions) will count it in its executable file search path. and also "lib" dir, "game" dir, "opt", "tmp"etc, etc. These are standard dirs in "/" dir.
Usually I keep my exec scripts in my ~/bin dir
a ~/tmp dir to compile oss souce packages.
a ~/opt dir to install the compiled packages
if you happened to configure some software package with prefix of your home, it will automatically create these directory for you: "bin" "lib" "libexec" "etc" "var".