there are a couple of main ways:
1 – connect the flash together by wire/leads
2 – use a wireless system.
I have used both and found both methods work well. I find a wireless system more convenient especially when you have 4 or more flashes.
Have a look at the https://www.dropcontroller.com/adding-more-flashes-flash-trigger-multipliers/ This shows the methods I have used including a small flash trigger multiplier I built.
For wireless you only need a basic trigger system (no need TTL/auto exposure) and use the flashes in manual mode.