The first thing that you want to ask yourself is what kind of database do you need? Does it need to be a very complex database such as one that compares scientific samples? Or does it simply need to be a large spreadsheet type database? If you need a database built, you will need to find a programmer who can do so for you. Otherwise, you will need to find a freelancer who has experience creating and managing large spreadsheets.
What do you plan on putting in this database? For example, a non-profit might want to keep information about its donors. So, this database might require columns for the name, address, email, amount donated, date donated, response sent, and more.
You also need to have an idea of where the freelancer will find this information. For example, you might have an electronic record of your donations, but they are not easily accessible or comparable. So, the information in your records will need to be transferred into the database.