Question: How did the streetcar, phone booths, and vending machines end up in the digiworld?
Answer: People who built the digital world most likely had them sent there. Gennai tells the kids in the last episode that the streetcar was from San Francisco, and he asked them to take it back for him.
Question: Why are Digimon called digital monsters? They don't look digital.
Answer: Digimon started as a series of virtual pets, making them digital. In the television series, Digimon live in the "digital world."
Answer: We are never told as to how they got there.