Google Fonts are free for both personal and commercial use. That means you can download and use them in your projects without having to ask permission or pay license fees.
Downloading the fonts is simple, you can either download them one at a time or all at once.
Downloading a Single Font
To download a single font, first, navigate to fonts.google.com and choose a font by clicking the red plus sign.
Clicking the black horizontal bar in the bottom of your screen will reveal more information about the font(s) you have selected:
In the top right you will see a red download icon, clicking that will generate and begin downloading a .zip file containing the fonts you have chosen.
Downloading All Google Fonts
A zip file containing every Google Font is available from the official repository.
Download Link: https://github.com/google/fonts/archive/master.zip
Note: The .zip is over 300mb in size and will be even larger when uncompressed.