There's a couple ways to 'bye' in Spanish, and I'll tell you about all 4 of them. The first one is 'hasta luego'. It's pretty formal, but it's used in informal locations, as well. The second way to say 'bye' in Spanish is 'adios'. That's pretty much the most popular version, or the most common version. The third way to say 'bye' in Spanish is 'chao'.
Some people in countries, like for example Uruguay, Argentina, Paraguay, they might say 'chau', with a U at the end. You'll hear the difference 'chao' or 'chau', but it means the same thing, it means 'bye'. The last way to say 'bye' in Spanish is 'nos vemos'; a way to say 'I'll see you later'.
That's 4 different ways to say 'bye in Spanish: Hasta luego, adios, chao or chau, and nos vemos.