Pro Micro RP2040 Hookup Guide
bboyho 
UF2 Bootloader
The Pro Micro 2040 is easy to program, thanks the UF2 bootloader. With this bootloader, the board shows up on your computer as a USB storage device without having to install drivers for Windows 10, Mac, and Linux!
What is UF2?
UF2 stands for USB Flashing Format, which was developed by Microsoft for PXT (now known as MakeCode) for flashing microcontrollers over the Mass Storage Class (MSC), just like a removable flash drive. The file format is unique, so unfortunately, you cannot simply drag and drop a compiled binary or hex file onto the board. Instead, the format of the file has extra information to tell the processor where the data goes, in addition to the data itself. For more information about UF2, you can read more from the MakeCode blog, as well as the UF2 file format specification.