To a lesser extent, it can also mean that something has arrived. For example, after a long training run, you and I are resting on my front poach. I say, "Gee, a cold beer right now would be great!" My thoughtful wife then appears through the front door, with two large, ice-cold beers, and says, "Here we go!" Ditto with ordering dinner at a restaurant, as the food arrives, or at a birthday party, when the cake appears.

Jacob big thanks !

It means something is about to start. It can be used when beginning pretty much any task, but it often (not always) carries the nuance that task will be either difficult or long. It can be used when departing on a long road trip, starting a difficult test, attempting something for the first time, etc. Hope this helps! Jacob