SPID, the Public System of Digital Identity, is a technology used to access the Internet and the IT servives of the Public Administration with a single ID and password.
A SPID Identity can be used to login on UniTrento's online services: Servizio SPID
For further information, please go to: https://www.spid.gov.it/
Yes, you will use your UniTrento password because all Google Apps for Education services are based on our authentication systems.
No. Both allow you to get a new password, but in different situations.
When changing the password, you must know your current password and set a new password.
The reset password instead allows you to get a new password, in case you have forgotten the current one. For this procedure it is necessary to have linked a private e-mail address. If the link does not exist, contact account.help [at] unitn.it.