Hey, in the new action economy readying an action is a simple action it takes 1 out of your 3 actions. It says, "ou must have enough acts left to complete the action you ready." does this mean that I would need to use 2 actions plus my reaction to use a readied action or just 1 simple action and my reaction. For instance a fighter readies an action to hit a monster when it approaches to ready it takes 1 simple action and then when the monster comes does the fighter hit as a reaction or does he need to have a simple action unused to be able to hit, apart from the reaction and the previously used action on readying.
also for instance would a caster that casts a spell which takes 2 acts not be able to ready an action to move if a foe comes to a certain area?
To answer your example, it will cost the Fighter 1 act and 1 reaction in order to perform that readied action. The "you must have enough acts left to complete the action you ready" clause is for more complicated acts that you can do to ready, like Grapple or Cast a Spell.
My question to add on top of that is whether or not that Readied Attack is at your highest attack bonus or not. If so, low-level combat could be even more lethal for unarmored spellcasters. Something like this:
Fighter vs. Sorcerer
Fighter's turn:
Move to engage.
Attack.
Ready an act (Either 5-ft. Step or Attack if he moves away).
Sorcerer's turn:
5-ft. step
Fighter either attacks again (at highest attack bonus???), or moves closer to Sorcerer
Sorcerer must either Concentrate to cast, or move 5-ft. again to disengage.
Rinse and repeat.
This begins at level 1, and this is only considering 1 opponent.