Help for a first-time administrator

There will be a lot of noob questions in here since I’m new and am suffering hard from imposter syndrome.

I’ve just taken a role as a sys admin (and also help desk tech really…) at a relatively small company, where I’m the sole in-house IT guy.

Without giving away compromising details, we have 1 server which is a file server and domain controller. Upper management would REALLY like to get rid of the server and go totally cloud-based, which we don’t have much of a choice to do since we are downsizing and moving to a much smaller space with no server room.

Being that I’m new to the administrator position (less than 3 years of help desk experience 🥲), I have no idea how we would manage user accounts or if “joining a laptop to the domain” would be a thing without a domain controller or any on-premises servers. We can leverage the use of a contracted IT company, but upper management would like me to take lead on it all, and I have no idea where to begin.

Can someone educate me on what the choices are? How are users and groups managed without AD? How do I reset their passwords, delete users, etc? Does Azure AD have all that functionality?