How to use [join]

The reference page of join has its arguments, constraints and declaration.

Joins all child [fork] invocations, implying the slot will wait until all forks directly below it has finished executing, and automatically copy the result of the [fork] into the original node.

join
   fork
      http.get:"https://servergardens.com"
   fork
      http.get:"https://gaiasoul.com"

As an analogy for what occurs above, imagine the two rivers from our above [fork] analogy that forked from one larger river into two smaller rivers, for then again to join up and becoming one large river again further down.