Hi Carol
So, just a quick explanation of RAM first . . .
All your files, applications and Windows are on your hard drive
When you start your PC, the Windows files are copied into RAM, that in Windows 10 is approx 1.5GB - 2GB of RAM Used
Then when you open another application, that is copied into RAM along with any other files you have open
So, if you purchase a PC with 4GB of RAM, that is the bare minimum for Windows 10, because when Windows is loaded, approx. only 2GB of RAM are left free, and that is not taking into account Hardware reserved RAM
Also Web Browsers are among the heaviest applications on your PC in terms of RAM, if you had maybe 4 or 5 pages open in a web browser, that may take up another 0.5GB - 1GB of RAM
So, to be honest, you can get by on 4GB of RAM, but 8GB would be a lot more suitable to Windows 10, which is very resource hungry . . .