I didn't even check after I signed up on Tuesday, but I just checked the bottom of Gmail and it says that I have use 3% of 65 GB, so I know I'm good. It may take a few days for the space to show up, maybe.
In the Google Drive app: 3 vertical dot menu > Settings > swipe up to see Storage.
In the full web version of gmail (on a computer), scroll down to the bottom of the mail, it shows "x.xx GB (x%) of yy GB used." "yy" will be either 15 or 65 unless you have already paid for different storage.