What do you want to know - origins, temperament, suitability as a pet?
Although many are purebred, they are not a recognised breed in the UK, so might have any other breed in their make up or recent pedigree. Originally they were black and tan but you can get them in all black, all brown or black and tan, and they can be smooth coated or rough coated. They stand about twelve inches at the withers (top of the shoulder) although this can vary depending on what sort of prey they were bred to hunt. They are a real working terrier. They need a lot of exercise and can be a bit sharp with other dogs so need firm discipline from a young age. They can also go after cats or other small animals.
Perhaps not ideal for a first time dog owner, and although generally good with children, they may need to be watched if there are kids running round screaming and shouting.
Definitely not a good idea if you have not got the time to devote to their care and exercise, certainly not a breed to just lie about and be a lap dog.