Use it when somebody has copied material you own and posted it somewhere with a provider you can reach: your photographs on a competitor site, your copy reproduced on another business page, your product images used in a listing that is not yours. The provider might be a web host, a marketplace, a social platform, or a search engine, and most publish a specific process and a designated contact for exactly this.
The notice has required elements and omitting one gives the provider grounds to ignore it. Identification of the work you own, identification of the infringing material with enough specificity to locate it, your contact details, a statement that you believe in good faith the use is unauthorised, a statement under penalty of perjury that the information is accurate and you are authorised to act, and your signature. Most platforms provide a form that collects all of this, which is the easiest route.
Consider a direct message first in many cases. A substantial share of copying is done by somebody who did not think about it, often a contractor building a site, and a polite email frequently resolves it within a day without a formal process. Reserve the notice for cases where that fails or where the copying is clearly deliberate.
Be careful about sending one where you are not certain you hold the rights. A false statement is made under penalty of perjury, the recipient can file a counter notice, and misuse has produced real consequences for the sender. The situation to watch is material a contractor produced for you where the copyright was never assigned, since you may not own what you are claiming.
If the copy is genuinely damaging and the provider is unresponsive, or the infringer is outside the reach of this process, that is the point to take advice rather than escalate alone. For most first year businesses the realistic outcome is a removal within days through the platform process, which is proportionate to the harm and costs nothing but the time to file it.