OK now that you have Arduino IDE set up, drivers installed if necessary and you've practiced uploading code, you can start installing all the Libraries we'll be using to program it.
There's a lot of libraries!
Open up the library manager...
And install the following libraries:
This will let you light up the LEDs on the front
Adafruit DMA NeoPixel
This adds a special NeoPixel library that uses DMA so the NeoPixel stuff happens without processor time taken.
Adafruit Unified Sensor
The underlying sensor library for ADXL343 support
This will let you read/write to the onboard FLASH memory with super-fast QSPI support
Adafruit Zero DMA
This is used by the PJRC Audio Library you'll install later.
This is also used by the PJRC Audio Library.
Our Keypad support library (for reading the button matrix)
So you can have the Trellis M4 act like a MIDI device over USB
The ADXL343 Library which provides accelerometer support
The NeoTrellis_M4 Library that handles MIDI, LEDs & button presses
Our fork of the PJRC Audio library to support the SAMD51