I can't figure out how to connect my brother printer via air print

Hi,

Any information about the exact printer model?

Generally speaking, you would have to begin by connecting the printer to a network (Wi-Fi router). This could be wirelessly, or wired (Ethernet), depending on the printer model. The Mac computer must be connected to the same network.

After this, you can add the printer using AirPrint.

About AirPrint - Apple Support

Add a printer to your printer list so you can use it on Mac – Apple Support (UK)

Run the Brother iPrint & Scan App, in lower right corner click on Select your Machine... does that find it or not?