How am I using so much data?

[James Bond]

Lay man explanation of 1MB.

Consider an A4 printed text which may contain 27-30 lines and each line may contain 72 characters.
Two store 1 symbol we need 1 byte. Thus, to store one A4 size we need=72*30=2160bytes
1024Bytes is 1KB. Thus, we need approximately 2 KB to store an A4 size matter. In reality, some compression methods are used which stores mother than this

1024KB = 1MB. Which means app 500 pages of A4 size pages info can be stored in 1MB
Similarly you can extend to 1GB ITB
1024MB=1GB
1024GB=1TB
1024TB=1Peta Byte