4 pin fan and servo

Hi.

I'm updating a former co-worker's project.
He used a servo motor, and the plan is to now switch for a fan.

1- Can someone explain me the best way to connect a 4pin fan to Arduino? All the schematics I find are really confusing. :~

2- Is it possible to use the same code from the servo operation to the fan?

(btw, this is quite urgent, so please help meeeeee)