"I want to create an application that generates a QR barcode, saves it with a person's name, and then stores the person's name and their corresponding barcode in a Firebase database. After that, I want to be able to scan the barcode and retrieve the data associated with it to check if it exists in the database.
Not sure I understand the reason for the QR code, you already have the name and data. Why not just select the name from a list, and return the associated data?
I have a small party with personalized invitations, and I want an app to manage the guests. Each guest should have their name and phone number stored in the guest list, and I'll give each invited person a barcode so they can enter the party. When the guests arrive, I'll scan the barcode given to them to ensure they are on the guest list."
Which is why I asked where the barcode will be scanned from....
How will the party-goer get their barcode, via email?
Seems you need a pen and paper to work out the workflow of your app from beginning to end, then to start, step by step to build your app with layout and blocks, then come back when you get stuck. You may not actually need firebase if only one device will be used to scan the barcodes at the party....