To use Google Apps on your mobile device - smartphone or tablet - you will have to download them from your App store. As I already mentioned on the Home page, I use iPhone and iPad, and will be showing examples on those devices. But I do expect that the Google Apps for Android will be very similar; if you have an Android and want to help, I'll be happy to work with you to show examples on this site.
These are the apps that I use often:
I personally use the Mail and Calendar app from my iPhone, and don't see any reason why I would want to switch to the Google versions. They exist, but I don't use them.
I have a few other Google Apps (Maps, Translate, Voice), but I don't use those for my volunteer work.
So, go ahead and download at least the first three (Drive, Docs, Sheets) now. They are free, and you'll be glad you did. Here's what they look like on my iPhone, at the lower left: