Is the "appleuser" login the same as the computer login?

The main reason I purchased this IMac was because while I used a PC, almost every day when I was all ready to start my online work my computer would be different then when I left it. I sell clothing and kitchen wares online. My files were scattered and my listed folders for each site were empty and some of my files were put back into the sell folder. I had to spend sometimes 2-3 days setting up my folders again before I could do any work. I tried to change many settings to keep out the cloud or AI (AKA NSA data storage facility). Next time I tried to change the settings they were gone. I tried my password, the appleuser password to change settings on my imac and I could not log in. I MUST have my files in the order I NEED THEM! I've been dealing with this for 2 years. I use to work at a computer store building, installing configuring, repairing etc. I have never had problems up until a couple years ago. This Imac is doing exactly what all my PCs were doing before I dumped them. How can I do my work when this randomized system is impossible to keep out of my files and folders?

I am a disabled veteran with a lot of problems. My fixed income pays my rent. When I do not sell anything I do not eat. This month is the first time since I was in my twenties that I am overdrawn in my bank. I'm having to pay hundreds of dollars in penalties over this i ssue. Are there any actual computers left or is this all the "peasants" get? How do I shut it off?