You can find pip in Path_to_Python_Home_Directory\C:\Python34\Scripts\pip.exe
Since you added a path environment variable to Python, I suppose you know how to do it for pip :)
Now you can install selenium this way: Path_to_Python_Home_Directory\C:\Python34\Scripts\pip.exe install selenium, OR: pip install selenium if you set its path environment variable.
I hope this helps!