When installing or upgrading to Windows 10, there are a few gotchas as follows...
First, backup everything you value.
Windows 10 should upgrade safely from Windows 7 and Windows 8.1 but there are no guarantees.
Do not tell Windows 10 your email address or anything about you, at installation or later.
After installation, turn off all the privacy-busting options.
Click Start (or press the Windows key) to switch between apps and the desktop. The desktop is more familiar.
Avoid downloading apps from the Store.
Normal software is generally available free to do what you want,
for example VLC instead of Media Player, GIMP for PhotoShop.
On earlier editions of Windows, you can tap F8 while the PC is starting up to go into 'Safe Mode' for repair and recovery purposes.
Right-click Start, choose Command Prompt (Admin) and in the black screen enter:
Windows 10 works like Windows 7 but slightly better, and Microsoft has promised free updates 'for the supported lifetime of the device.'
Note that Microsoft by default decides when to update your PC, and Microsoft alone decides when your PC's life is over! See The next generation of Windows - Windows 10.