Vietnam is a long, narrow country curving down the eastern edge of mainland Southeast Asia — often described by its own people as shaped like a carrying pole with a basket of rice at each end. Those two "baskets" are the Red River Delta in the north and the Mekong Delta in the south, and much of Vietnamese history has been shaped by the space between them.
Today roughly 100 million people live in Vietnam, and several million more live abroad in what is usually called the Vietnamese diaspora. Vietnam officially recognizes 54 ethnic groups. The largest by far is the Kinh (người Kinh), sometimes called ethnic Vietnamese, but the country also includes Tày, Thái, Mường, Khmer Krom, Hmong, Chăm, Hoa and many others, each with their own languages, clothing, and traditions.
When people say "Vietnamese culture," they are usually describing something much more varied than a single set of customs. A family from Hanoi, a family from Huế, a family from the Mekong Delta, and a family that resettled in California in 1975 may share a language and a holiday calendar while doing many everyday things quite differently.
That variety is not a complication to apologize for. It is the actual shape of the culture, and it is where this course begins.