5e D&D (upon which the game is based) allows for characters to interchange their actions as long as non-allies don't come between them in initiative.
For example, if you roll a 20 on init, and I roll a 19, and a monster rolls a 17. You could take your bonus action, I could take my action, you could then take your action, followed by me taking my bonus action, then we both move - or any other combination - all before the monster gets to go.
Out of curiosity, where are you getting this idea and concept from? This is not a rule or even an optional rule in 5e - it's not in the PHB, nor is it in the DMG's optional combat rules. If I've forgotten something, I'd appreciate a reference for where you're getting this from; both the combat section of the PHB and the optional combat section of the DMG are and remain very clear that each player takes their turn individually, even if you're using by-sides initiative.
This is not to say that linked initiative of players is a bad thing, per se, and it has its benefits (as long as you don't mind enemy creatures getting those same benefits against you - i.e. pack tactics all the time for everyone, wolves, and so on), but it's not any part of 5e, formally.