Just what Ernie specified on his previous response privately, if you'll use our client libraries, then the access token will automatically be generated using the refresh token at the backend. However, if you are using other applications, you have to manually generate the access token on your end using the refresh token. As a general guide, you may refer to this
link to read more about authentication of the Google APIs.
Let me know if you have further clarifications or if I misunderstood your concerns.