Staff concept
You can hire different types of staff that'll give you an advantage in differnt areas of the game. To hire a new staff member from the transfer market, you'll have to pay a one-time recruitment cost, and once the staffer joins your ranks you pay wages at the end of each turn.

Wages (as well as the one-time recruitment cost) are dependant of the staffer's skill level at the time of recruiting him. If you level up your staffer, his wage won't rise. So it's often a good idea to hire an average staffer and level him yourself than to hire an extremly skilled staffer you have to pay high wages for.
Staff types
There are three different staffer types in the game :
Scientists
Every scientist you hire will add up to your global research factors as well as the scientific global project requirement factor, depening on his skills. Note that there is a cap for the research factors that's split between scientists and buildings, so hiring more scientists after reaching that cap won't make any sense.
Generals
The main use for generals is attaching them to your divisions (besides each hired general will also add to our global project requirement factor). Each general has three different skills that influence different values of the units assigned to your division. For more information on how a general's skills affect the divisions, see this chapter.
Agents
Each hired agent will add to the glboal project requirement factor, but their main uses are (counter) espionage and sabotage. You can either infiltrated enemy regions and do espionage and sabotage over there or assign them to your own regions for counter espionage. See the espionage chapter for more information.
Experience system


Similar to role-playing-games there is a levelling system for your hired staff. When you recruit a new staff member he'll start with zero experience at level zero. During gameplay certain actions will add experience to your staffer (e.g. winning a battle for your generals or a successful espionage action for your agents), and if a staffer has gained enough experience his level will increase (up to 9).

And with each increased level his whole skill set will also be increased, while his wages stay the same. So if you hire an average scientist and level him up to level 9 he'll have excellent skills with the same wage as when you hired him, making skilled staff very valuable. So especially for agents or generals, that can be lost during gameplay, it's a good idea to keep an eye on and not to loose them.

An additional way of increasing staff experience is training. You can initiate different staff trainings for either one staff type or all, increasing their experience. Though these trainings are pretty expensive and lower staff capabilities as long as they're run.