In general, ActionScript executes in a top-to-bottom, left-to-right order. That is, each line executes one after another, working from left to right. Several things can change this order in subtle ways, but it’s basically a reliable rule of thumb.
For example, subroutines of one type or another can be called in the middle of a script, causing the execution order of the original script to pause while the remote routine is executed. When the subroutine has completed, the execution of the original script continues where it left off.