How to perform a Distributed Denial of Service (DDoS) Attack:

1. Gain control of hundred or thousands of networked devices. This may seem hard, but on the dark web there are already “botnets” of millions of compromised devices (webcams, thermostats, PCs, etc) whose owners don’t realize are compromised, and you can “rent” out the use of thousands of them pretty cheap for a day or so. The “lender” (who has garnered all of these compromised systems by infecting them with malware) will give you the scripts to run that will contact ALL of them in minutes, upload the IP address of the site you wish to attack, what sort of attack (packet-flood) to perform, and when.
2. Pull the trigger. Suddenly thousands of devices are each spewing out million of packets per second against the site of your choice, choking its network interface and rendering it useless for legitimate users.

See how easy that was?