Just choose which country you want and click the button. Pick whichever location is closest to you, or actually closest to where the content or service you are reaching sits -- for most people that is the same thing, but it is not always, and the account works the same regardless of which one you choose.
Vless is the lighter successor to Vmess: it drops the built-in encryption layer and the timestamp check and leans on TLS for both. Less work per packet, which shows up as slightly lower CPU use on the phone and a little less latency.