x64 and x32 mean the droplet is 64 or 32-bit respectively.

6 or 7 are the CentOS version number.

There's almost no good reason to pick 32-bit anymore.

Thanks. The page at https://www.digitalocean.com/community/tutorials/how-to-create-your-first-digitalocean-droplet-virtual-server says "A 32-bit operating system is recommended for cloud servers with less than 3 GB of RAM -- this is especially true for servers with 1 GB, or less, of RAM." I'm so new I squeak and am starting off small so I thot 32 would be the best option.

I honestly dont think it matters too much to be honest.

if you are not getting much traffic and/or are not doing anything too taxing then 32bit is fine,

That said,
Every server I build now is 64bit no matter what just because.