.bash_profile resides in your user folder. To create a file (hidden or visible) simply enter touch:
touch ~/.bash_profile
A dot prepending the file name makes the file invisible.
Then open the file with nano and add the line:
nano ~/.bash_profile
Save the content with ctrlO to disk and exit nano with ctrlX
Afterwards you have to source the modified or new .bash_profile file to immediately reflect the changes:
source ~/.bash_profile
A different method (and a one-liner) is:
echo "export PATH=/usr/local/gnupg-2.1/bin:$PATH" > ~/.bash_profile && source ~/.bash_profile
This will overwrite any content in .bash_profile
To append a line in an already existing .bash_profile file use
echo "export PATH=/usr/local/gnupg-2.1/bin:$PATH" >> ~/.bash.profile && source ~/.bash_profile