Autoruns is a very useful tool.
Most necessary instructions are on the same page where you find the download link.
The current version (14.09) has some changes from the version I have currently installed (13.98). These appear to be mostly cosmetic. In the image below, v. 14.09 is above v. 13.98, and you can see that some of the menu icons have changed and a few have been added. If you hover above an icon, you'll see a pop-up explanation. Among other things, there's an icon to hide any entries that have been cleaned by VirusTotal.
Also, in 14.09, the "Help" link appears to be directed to the download page (https://learn.microsoft.com/en-us/sysinternals/downloads/autoruns) rather than to the Help file as in the earlier version. I expect this is a bug that will be fixed shortly.
As far as the files contained in the downloaded ZIP file are concerned, I don't know what the two with the "a" suffix are. They both fail to run on my system, giving the error "___ is not a valid Win32 application."
The files with "64" are 64-bit versions. If you have a 64-bit version of Windows, you can run either the 32-bit or 64-bit version of Autoruns.
The files with "sc" are the command-line versions, as explained on the download page.
If you need more information (and you really don't), ask here: https://learn.microsoft.com/en-us/answers/topics/windows-sysinternals-autoruns.html