I am having some issues in loading IDE on my arduino and sucessively I frankly don't know how to load GBRL, in both case some passwords are requested and I don't have them, pls someone may be so kind to explain step by step how I can load those programs. Thanks

Please provide more information about the problem. The Arduino IDE will never ask you for a password, so that must be coming from somewhere else.

GRBL and or the IDE should not require any passwords.
Only exception I know of is if you are trying to use the ONLINE IDE "CREATE".