I’ve never been to New Orleans. But I have celebrated Mardi Gras. Sort of.
Carnival has been celebrated for centuries in the West Indies, especially in Trinidad and Tobago. The islanders used Carnival to mock and imitate the pre-Lenten traditions French plantation owners brought to the islands. The Carnival season begins after the Epiphany and culminates the day before Ash Wednesday.
After the abolition of enslavement of Africans, the fete (a West Indies word for party derived from French) only got wilder with an absolute eruption of energy, bright colours and soca music that brings the streets of the major island towns to life. They are planned months in advance. The food and alcohol flow freely from establishments, and street carts are set up every couple of metres. Revellers are entertained by many music competitions, sports games and costume competitions. In the West Indies, our massive carnivals add a particular vigour that makes it much more fun than New Orleans for the celebration.
J'ouvert (a gallicisation of jou ouvè or "daybreak") is the unofficial start of Carnival, which takes place the Monday before Ash Wednesday. The biggest day of the Carnaval celebration is Mardi Gras (Fat Tuesday) when the King and Queen of the Carnival are crowned, and everything goes out with a bang. Mardi is the French word for Tuesday. Gras is the French word for fat.
I'm unfamiliar with what happens before and during Mardi Gras in New Orleans. But in celebration of the day, I made a Sazerac, which [according to this website, is "..the official cocktail of New Orleans".