UPDATE: vBooter's new domain name is vbooter.pw!
In order to initiate an attack, you need to know the IP address. If you already got it, navigate to the stresser's hub.
On the host's field type the IP address that you want to take down.
Below type the port to attack on the remote server. Use port 80 for a website or for a home connection or find an other port from this list (such for Minecraft).
And then on the time's filed enter the duration of the attack in secods. The recommend value is 60 seonds. That means that vBoter will attack on this IP adress for one minute in order to take it down. As a free user the maxinum attack time is 320 seconds (5 minutes and 30 seconds).
For the attack types, refer to this article.