This program prompts for a source and a destination IP. It checks if the source is set to zero so that it randomizes an IP. Otherwise, it uses the IP its user provides. It then sends out TCP connection request to a target system, which is usually a Web server or a SMTP server that a remote user attacks/floods. The source system receives the TCP connection request from the target host.
When the target system responds to the TCP connection request and the source system IP is invalid or randomized, the target does not get a connection established. Instead, it continues to attempt connection and opens a process with every attempt. It does not close all the active connections so that the target system slows down, or hangs or even crashes.
This type of DoS is called a SYN flood.