A more thorough explanation:

A letter of credence is a document that is used in international law to accredit a diplomat to the government of the country where they are being sent. It is also known as LC or L/C. The letter of credence is usually presented by the diplomat to the head of state or government of the host country.

When a new ambassador is appointed to a foreign country, they are given a letter of credence by their own government. This letter is then presented to the head of state or government of the host country to formally introduce the ambassador and to establish their diplomatic credentials.

For example, if the United States appoints a new ambassador to France, the ambassador will be given a letter of credence by the U.S. government. The ambassador will then present this letter to the President of France to establish their diplomatic credentials and to begin their official duties as the U.S. ambassador to France.

Another example is when a foreign head of state visits another country. They will usually bring a letter of credence with them to present to the host country's head of state or government. This letter serves as a formal introduction and establishes the visiting head of state's diplomatic credentials.

Overall, a letter of credence is an important document in international diplomacy that helps to establish the credentials of diplomats and other officials who are sent to represent their countries in foreign lands.