A good place to start is to get the blink sketch working as described here: Getting Started with Xiao nrf52840
Next, you could get an IMU example working as described here: IMU Usage
Ignore the .cfg file. That is an alternate way to flash the firmware. I got tired of hitting the tiny button on the Xiao. The above two links should cover the rest of the questions. At least get you closer.
I’m using the latest Seeed nrf52 board package: 1.1.3