whats is the use of righgts management adhoc license?
Do i need to assign this to enabe RMS to e3 users?
It's the "self-service" or "viral signup" type of service, meaning that any user in the company can provision it and its free. If your users are already licensed with E3 or equivalent license, you can simply ignore this one. More info for example here: https://docs.microsoft.com/en-us/azure/information-protection/understand-explore/rms-for-individuals