Copy the vless key (starts with the characters vless://, copy them too) that you were given. Where to find vless keys: in the email with the key, there is a link "[VLESS keys]" below the main key. You can also get your vless keys here: https://vless-premium-web.com/key/ (enter your primary access key there)
In the v2raytun application, click on the “+” on the top right and either paste manually or paste your key from the clipboard.
The configuration will appear in the list below: click on it.