The difference is that the system reads @ symbols as “full stops” or "complete this line before the script moves on. The & symbol is read as “can be played with the next line” or if used after an @ line, this line can be read immediately following the completion of the @ line.
Example explanations:
@COLE walks to spot x y in zone z in 3
COLE (talk_greet_neutral)
Hello, everyone!
&COLE starts idle_handsonhips_netural_loop
^^ My “walks to” code will play out first then I will greet everyone and as soon as I greet them and my speechbubble is tapped, I will put my hands immediately on my hips.
&COLE walks to spot x y in zone z in 3 then COLE starts idle_loop_rear and COLE faces left
EVE (talk_handsonhips_neutral_loop)
I can’t believe Episode has taken this long to put out a new contest.
&EVE starts tinker_stand_neutral_loop_rear
^^ I will walk in while EVE is talking and tinkering - and by adding the then blah blah to my walk code, I’ve given my entering character something to do after reaching their spot. 
Hope this helps