1) windows: PATH | grep -oP ".composer.*bin"
If it's in the path You'll get a response if it's not you'll get nothing.
2)
~/ refers to home path on linux doing %HOMEPATH% on windows results in the same thing, which in your case would be %HOMEPATH%/.composer/vendor/bin
Doing /somefolder Will go to the root path in linux and try to find a folder there called somefolder but won't do anything in windows, I'm not sure what the equivalent in windows is, might be referring to root of the drive, I.e. C:\ or D:\ etc.
To add .composer/vendor/bin to your home path you need to go to your environmental variables and add it into the path you can go here and follow the steps in the answer or the question.
The important bit:
Example of windows SETX command:
Print the PATH environment variable:
C:\Users\Charity>echo %PATH% C:\windows\system32;C:\windows and
space;C:\foobar Use setx to set the environment variable:
C:\Users\Charity>setx PATH "%PATH%;C:\zombiepoke" SUCCESS: Specified
value was saved. Close and re-open cmd terminal, then run:
C:\Users\Charity>echo %PATH% C:\windows\system32;C:\windows and
space;C:\foobar;C:\zombiepoke You have to be careful with double
quotes. If you let quotes get into your path variable it might break
something. However they are necessary for specifying addendums to the
original %PATH%.
Make note though that this only sets it for the current user context, to set it for all users you have to to use setx /M.