Building Up From the Byte
All digital data is measured in bytes. A byte is a small group of bits, the most basic units of information a computer works with, and a single byte is enough to store something simple, like one letter of text. Files, photos, songs, and apps are all just very long strings of bytes. Because bytes are so small, the units used to describe everyday files are scaled-up versions of the same idea.
Kilobyte, Megabyte, Gigabyte
A kilobyte is roughly one thousand bytes. A megabyte is roughly one thousand kilobytes, or about one million bytes. A gigabyte is roughly one thousand megabytes. Each step up the ladder multiplies the size by about a thousand. So when a photo is described as three megabytes, that means it is made of about three million bytes of data. When a phone has 128 gigabytes of storage, that is about 128 billion bytes of room for everything it holds.
Where You See It
Megabytes show up everywhere once you start looking. A song or a high-quality photo is typically measured in megabytes. App sizes and downloads are usually listed in megabytes. Mobile data plans, file attachments, and storage figures all use the same scale. Knowing roughly what a megabyte means turns those numbers into something you can actually compare: a one-gigabyte video is about a thousand times bigger than a one-megabyte photo.
Source
This article was written using information from Wikipedia.