The alphabet is the letters which make up a language. Different languages each have their own alphabet with its own specific history which suits the sounds and needs of that particular language and the people who speak it!
The alphabet has a very old history, so there are some different ideas and theories among those who have studied and traced its origin. Most agree that the use of an alphabet, or at least characters that represent words or ideas, is a practice that’s been around since the ancient Egyptians, who used a special system called "hieroglyphics". However, alphabets more similar in use and form to the ones we know today are usually traced to Greece, since the Greeks were the first to include vowels in their alphabet and not just consonants!
Depending on where they came from and when they developed, some alphabets (like English and Spanish) are very similar while other alphabets (like Russian) look very different!