Download and Double Click to "Burn" the ISO to a CD. I made this "generic" Windows PE disc from the info I found on the YouTube video "Create a Windows 7 PE with Make_PE3 by Britec" using a program called "Make_PE".
Want to make it a bootable USB? Use "Rufus". A guide to using it is on YouTube video "Run Hiren's Boot CD from USB Flashdrive by Britec"
Almost nothing! Please don't download it for no reason, you'll cap the bandwidth. However if your PC won't load Windows, you can boot the computer, and then do things to fix Windows. Like "copy over the files needed to fix the Windows XP error ntldr is missing", or "Use Bootrec.exe in the Windows RE to troubleshoot startup issues".