In its simplest form, you have a table with one Header Row. In each Header cell you place the name of the field that you are going to fill-in for each of the records in your database.
Then you proceed to use one of the rows below to describe each item in your database.
You will create other tables to extract specific records or summaries from the main table.
You can do mail merge from this data to Pages to create custom reports. It's pretty flexible, but has nowhere near the power of a commercial RdB.
A "database" is simply one or more tables of "data", so creating the database is really the simple part (although it does require planning to fit the capabilities of part 2).
What you're asking is part 2, 'how do I create a "database front end" or 'how do I manage a database" using Numbers.
For that, the answer is "it depends." It depends mostly on what you need the database to do. If you can express those needs in specific terms, there are people in the forum who can help you find how to make Numbers perform the function, or who can tell you it can't be done (and then, occasionally, be proven wrong 😉 ).
Numbers has several tools for managing a list, but if your DB goes beyond being a single-table list, Numbers is often not up to the job.
Bento 3 (from Filemaker) adds some DB management capabilities, and works with data stored in Numbers documents or in Address Book.
After that, there's a huge step up in complexity (and cost) to FileMaker Pro, which, as the name implies, is a 'professional' application capable of creating management systems for huge and complex databases.
Along the way, there are the database modules in the open source productivity applications OpenOffice.org, NeoOffice and LibreOffice (all variants of OpenOffice,org, all free to download and use—although donations are requested). For the first, the name is also the website; for the others, add .org to the application name.
Two cautions on these: The (database) learning curve is pretty steep, and the documentation was pretty spotty the last time I looked.
