Text - book might be around 1MB or so ( each byte = 1 letter/character, so 1 page might be 2-3KB, times 300 pages = 1MB, text only, no images)
Photos - around 1MB per image (6 megapixel camera, good quality JPG), or 6-10MB for the "RAW" lossless format
Music
MP3 - 5-10 MB per song, but depends on format, bitrate.
WAV (uncompressed) about 40MB-ish per song
Video - tens or hundreds of MB per minute, and several GB for full length movie (good quality)
CD = 650MB, holds a typical (WAV uncompressed) music album of 10-15 songs, or if you burn MP3 you could fit roughly 100 songs
DVD = 4.7GB, holds typical full length movie of 90-120 minutes
1KB - around a half a page of text
1MB - an entire book (text only), one photo (JPG), or less than a minute of MP3 music
1GB - a highly compressed (lower quality) movie, or a high quality 20-30 TV show
1TB - hundreds of movies, millions of photos, every book (text only) in your public library?
So text files are typically measured in KB, images in MB, music in MB or tens of MB, compressed video clips in 10's of MB, and high quality video in 100's of MB or in GB, depending on length
Above are all very rough, pls don't nitpick my estimates or I will sulk.