Can't keep Multiple apps/programs open on screen at same time.

I have two monitors. On #1, I have a Safari website open, plus two Finder screens - sized and positioned so I can click on any of them at will to work in. On #2, I have a program open plus a Pages document, also sized smaller and positioned so I can actually see the full content of both. /// Something happened the other day and now I can't get the same result. When I click on the Safari website, the Finder screen minimizes and retreats to the monitor's side as a 1-2 inch tiny representation of it. On Monitor #2, when I click on my Pages document, the other program minimizes and retreats just the same. -- I'm sure I re-set something in one of the dozens of settings. Been trying for two days to find out what happened. - I see talk of Spaces, Tabs, Mission Control, I do not know what I did. Please tell me what setting I need to change.