Use blockchain to store data
Blockchains, by design and definition, defines a specific type of database… they are a write once read only database. What that means is, they are designed to be only ever created, and not edited or deleted.
This makes them immutable (ie unchangeable), and historically accurate (ie data entered and fixed in a certain point of time). You can think of it as an ever growing journal that is constantly having new pages added to it over time. This is the strength of the blockchain database design that has been effectively used to enable Bitcoin to be so effective as a money ledger.
The other core feature of blockchains is that it is secured by complex mathematics and distributed (many copies of the data stored across different locations) making it difficult (almost practically impossible) to manipulate / exploit.
This type of database is different from conventional databases, where data is housed in a certain data structure (like arrays or tables) and have CRUD (Create, Read, Update, Delete) operations, controlled through a centralised administration function, that is given to administrative users (ie default Admin users). This approach opens up the whole system (and database) to the end user, and requires the user to take responsibility for that system (including security, access controls and assigning CRUD capabilities.
If you understand these fundamental differences, it isn’t hard to use blockchains as a database / data store. In fact, for certain use cases (ie Bitcoin), blockchains are the perfect database, because they don’t trust central actors (ie financial institutions like banks).