Have you checked the documentation that is on the SD card that shipped with the unit? There is some documentation on there - it goes through the assembly, firmware updates, etc…
I’d also suggest you check:
Frame squareness
Check this thread for instructions Falcon 2, Frame out of alignment - #4 by jimandyen
All cables for bent pins
This seems to be an issue with many units where cables were “forced” in and resulted in some bent pins. That caused various issues like Laser immediately firing when the unit is turned on, axis not working, …
To do this validation, gently disconnect and visually inspect the pins on the various cables you have access to. If a pin is bent, “politely” un-bend it, but be extra careful as to not break it. Also, be gentle when inserting it back to ensure you don’t bend any pin.
For the rest, I think you’ll have to rely on the various videos you can find on YT - after looking at a couple ones, you should be familiar enough to jump right in.
Next step will be to pickup the software that suites you best (ease of use, and $) to drive your laser, or to generate G-Code files to put on the SDCard. Here, think of LaserBurn ($ but is complete and easy to use) or LaserGRBL (free but I haven’t tried it).
Good luck!