Incorrect install. How to back up personals and reinstall the right way!

After rigorous research I have determined that a fresh install needed. Using my SATA ssd as the boot,and the os and using my hdd as storage for my media, docs and any software not part of the os. I am dealing with efi issues, as part of partitions and currently EVERYTHING is running off my HDD, a large stress, dir's&files not where they probably should be and a large lack of permissions/ownership issues. I think the os itself is just not running efficiently and at it's best. Definitely not optimized for hardware! (with current setup)
I'm old school. I get the jive and am learning coming from the MacOS world. I am on a Mid 2011 I am using old hardware, the newest being the T7 I mention below.iMac and it has the fusion drive. It just took me 20 mins to figure out how to move this typing window up. Click the little blue line on the top and drag upwards. I don't think I have any directory set up, files all over, a SSD internal (part of the fusion sys) but all in all I have a 1tb HD, 256gbSSD, and an external 1tb T7 samsung to help. I'm lacking permissions, things just aint working right.
** I could get into my 1GHZ G4 perhaps another time.**