Updated : 2021
File explorer
browse to folder with TTF (or OTF etc) file
double click the TTF file
Click the install button at top of the opened application
Enter password for your admin account (if required)
click yes
The font is now available for use in Photoshop, PSP, Microsoft Word etc on your PC
** Please note this is for windows 10 PC (though the same approach should be available in earlier versions of Windows PC)