If you get your adb from Android Studio (which most will nowadays since Android is deprecated on Eclipse), your adb
program will most likely be located here:
%USERPROFILE%\AppData\Local\Android\sdk\platform-tools
Where %USERPROFILE%
represents something like C:\Users\yourName
.
If you go into your computer's environmental variables and add %USERPROFILE%\AppData\Local\Android\sdk\platform-tools
to the PATH (just copy-paste that line, even with the % --- it will work fine, at least on Windows, you don't need to hardcode your username) then it should work now. Open a new command prompt and type adb
to check.