If you have selected an OS template with VestaCP server control panel for your VPS, make sure to wait at least 5 minutes so it would finish installing.
Afterward, you can connect to your Vesta panel by writing your server IP address into your browser. You can find your VPS IP by going to Server Management area. For example, https://127.0.0.1:8083 where 127.0.0.1 will be replaced with your server IP address.
If you have not installed an SSL certificate to your VPS, you will see a security warning. Ignore it, proceed and you will see a login page.
There you can enter your VPS root username and password. If you don't remember your password, you can change it in your Server management area.