You (almost) certainly don't have 64GB RAM! RAM is your computer's memory, not its hard disk. The usual comparison is with a desk and a filing cabinet. You keep lots of paper files in a filing cabinet, just like you keep lots of digital files on a hard disk. The bigger the filing cabinet, the more files you can keep in it.
But, in order to work with a file, you need to bring it out of the filing cabinet and open it on your desk. When you open a document on your computer, that's exactly what happens - it is fetched off the hard disk and opened in memory. The bigger your desk is, the more files you can have open at the same time.