I don't have an admin account on my Mac. I don't know how it happened and now I want to add one because I cant do anything thing without it and I can't add a new user without an admin account.
OK - you don't need admin to restart, but let's get you an admin user anyhow. you need one and the time to do it is sooner rather than later.
This requires a restart to begin this process, please save your work and buckle up.
You didn't edit in what version, so we'll assume macOS Mojave version. You can always ask a follow on question if you discover you can't use the general advice. Be sure to list your Mac OS version, though or get local or Apple support if you can't find that out either.
- Might have accidentally change admin user to standard user
- New MacBook had user accounts already; I deleted admin and can't get back in
The first is how you can make sure you don't have some admin user you can reset the password, the next two have awesome answers that are basically the same.
Restart in single user mode and mount the drive and remove one file. That causes the next start to offer you to make a brand new admin account, not erasing any data - but just adding a new user / password you know to make your existing account an admin.