(new member +newb) How to create a timed turn battle sequence

So in the battle processing bit I was wondering how you could make it so when the battle starts the quickest player can attack however if they are too slow in choosing what move or guard etc they want to do the opponent can then attack. meaning they could potentially attack at the same time. 

^^ Essentially creating a slower combo system. 

Also wondering if you could create postions on the battler adding a bit of strategy to it.7

Please ask/explain in very simple terms, im still getting used to it and I havn't tried coding/scripting yet.