To minimize a window means to hide it. You will find yourself using a window's Minimize (dash) button when the desktop becomes cluttered with windows and you either can not see a certain window (because it is hidden/covered by another window or has been minimized already) or a certain window is partially hidden (as shown in Fig 1.1).
Fig 1.0 - The desktop is filling up with windows
In Fig 1.0 above I first opened the PICTURES folder (window), then Microsoft Excel 2016 and then Microsoft Edge. Hence why the first window opened (the PICTURES folder) is always at the back and the last window opened (Microsoft Edge) is always at the front. To go back and forth from one window to the next you have four options - although you might not use all of them.
The first option is to click on any blank part of a window (i.e. inside its Display Area), but preferably on its Title Bar (Fig 1.1 below), to make that window the front (top) most window. Whenever a new window is opened, or an existing one is clicked on, it becomes the front most window. Hence why the Microsoft Edge window above, which was opened last, became the front most window. If I click on the PICTURES window (folder) the order will be as follows: Microsoft Excel 2016 at the back. Microsoft Edge in the middle and the PICTURES folder (window) at the front. If all the windows are of the same size and in the same position (overlapping each other) this option can not be performed, as you would not be able to click on any window that is behind the front most window.
Fig 1.1 - Click on a window's Title Bar to make it the front (top) most window
The second option is to minimize all the other windows that are obstructing the window you want to use. So to get to the PICTURES window (folder) you would click on the minimize (dash) button of the Microsoft Edge window and then click on the minimize (dash) button of the Microsoft Excel 2016 window. However, this option is not ideal if you have more than five windows open simply because you would be spending all your time minimizing the other windows.
Fig 1.2 - Click on a window's Minimize (dash) button to minimize that window
The third option is a balance between options 1 and 2. First you need to click on the Show Desktop button, located in the bottom far right corner of the desktop screen (next to the Clock). It will automatically minimize all your windows and then show you the desktop only. All you need to do then is click on the taskbar icon of the window you want shown. In this example the taskbar icon with the Libraries (PICTURES) Folder icon. This will restore the PICTURES window (folder) back to the size it was before it was minimized. So if that size was maximized it will be shown as a full sized window, otherwise it will be shown at its custom size. To restore another window just click on its taskbar icon.
Fig 1.3 - Click on a minimized window's Taskbar icon to restore that window back to its original size
When you hover over a window's taskbar icon Windows 10 automatically previews that window, as shown in Fig 1.3 above, so that you can hopefully distinguish between two identical folders or web pages for example.
The final option is the same as option 3 except you do not use the Show Desktop button. You simply switch between windows instead by clicking on a window's Taskbar icon, to either minimize or restore that window, regardless if any other windows are minimized or restored already. So regardless if ten windows are blocking a window you want to use, you can simply click on its taskbar icon to either minimize it or to bring it to the front of all other windows.
When a window has been minimized (hidden) its taskbar icon will be dim. And if at least one other window is displayed, either maximized (full size) or restored (custom sized), the last/active window amongst the displayed windows will have a highlighted (brighter) taskbar icon. So in Fig 1.4 below all windows have been minimized and therefore have dim taskbar icons. In Fig 1.5 though the Microsoft Edge window is still being displayed at custom size (not shown here) and is also the last/active window, therefore it has a highlighted (brighter) taskbar icon to let you know this.
Fig 1.4 - These taskbar icons have been dimmed because all of the windows have been minimized
Fig 1.5 - The Microsoft Edge taskbar icon is highlighted (brighter) because Microsoft Edge is being displayed and is the last/active window
One thing to note is that the taskbar icons become highlighted (brighter) in the order you activate each window. So if you activate the PICTURES folder (window), Microsoft Excel 2016 window and then the Microsoft Edge window (so that Microsoft Edge is the last/active window) and then minimize the Microsoft Edge window, the Microsoft Excel 2016 window becomes the last/active window and therefore the only taskbar icon to be highlighted (brighter). In other words: Each time you minimize a window, the window that was active before it now becomes the active window again and therefore has the highlighted (brighter) taskbar icon.
The just said applies to a window's border colour too - When a window is the last/active window, currently being displayed, its border colour is light blue. However, when a window is inactive, but currently being displayed, its border colour is darker (charcoal/dark grey). So in Fig 1.1 above both the PICTURES window (folder) and the Microsoft Excel window are in charcoal (inactive) whereas the Microsoft Edge window is light blue (because it is the last/active window).
NOTE: If a window is open, regardless of being minimized (hidden/inactive) or displayed (shown/active), it will have a thin light blue line underneath its taskbar icon to denote its program or task (i.e. print job) is running; either in the background or foreground.