nRF Util's suit command is a CLI tool for performing a series of SUIT operations, such as inspecting SUIT manifest files or uploading SUIT envelopes.
The tool is meant for use with Nordic Semiconductor devices that support the Device Firmware Update using SUIT.
All nRF Util's suit subcommands (except for envelope-hierarchy) connect to a device over a serial port and then issue one or multiple commands to the device to perform SUIT operations over SMP over UART.
Before you use these subcommands, make sure you are familiar with SUIT basics and especially SUIT manifests.