The simplest form of computer database is the flat file database. Microsoft Excel can be used, and is used by many people, as a database. But this flat file database has serious limitations. One is its slow speed. Another is that a flat file duplicates a lot of the data that could be entered just once.
Duplicate data has to be input again and again.
It also has to be sorted by the computer program. Although the user doesn't know how it's storing information internally, it is stored in a very efficient manner and operates very quickly when properly designed. Microsoft Access is a relational database. See answers for more background on databases.