My Mac mini asks a password for every thing why

Sounds like you have a permissions problem.

I'm assuming you're working with documents inside your user folder?

If so, in Finder, open your disk to the root directory, eg. MacOS/Macintosh HD/High Sierra, whatever you have named it by double clicking the disk icon on your Desktop. Then double-click the Users folder. Then right-click once on your username's folder and Get Info, or normal click once and Command-i.

Then at the bottom of the window that pops up there are permissions. Click the little padlock once and enter your password.

Make sure that your username has read/write permission, you can change it by holding the mouse down when clicking on the permissions next to your username, change it to read/write.

Then click the little gear icon at the bottom of the window and select "Apply to enclosed items".

What type of documents are you trying to open/save/delete from which folder?