D&D 5E Action Surge Questions

[DEFCON 1]

So what can I do as a bonus action exactly?

The most common use of a bonus action for a weapon user is two-weapon fighting. The main hand attack uses your action for the round... the off-hand attack can be made using your bonus action.

Rogue also get Cunning Action which uses his bonus action, and many spellcasters have spells that only require a bonus action to cast.

 

[Paraxis]

Bonus actions were designed to be easy but I think they cause confusion in some players that played older editions. Unlike the action economy of 3e/4e with swift or minor actions, bonus actions are exactly that a bonus when you do something that triggers one.

So action economy of 5e is:
Action
Move
and possibly a bonus action if trigger one.

 

[PnPgamer]

In comparison for previous editions bonus action is comparable to swift action. You get it once during yoir turn and you got to use it on special cases. However these special cases seem to be more common in 5e.

 

[Athinar]

A secondary Weapon is just that case, bonus action

 

[Staffan]

I look at it as a bonus action being the same as a swift action in 3.5e/minor action in 4e, it's just that the default list of things you can do as a bonus action consists solely of "Make an off-hand attack with a light weapon, if you used the Attack action with a light weapon in your primary hand." Some class features, spells, and so on add to this list.