How exactly does a resistance reduce current? I've heard that resistors are used to decrease current to a particular appliance, such as in the regulator of a fan. However, I've also heard that the total current in a circuit is always the same- in other words, all the current leaving the positive terminal of the battery reaches as it is to the negative terminal. How can this be? The two statements are contrary. How can the total current be the same if a resistor is reducing current at some point in the circuit?
 A: Regarding what you consider to be a contradiction:

How can the total current be the same if a resistor is reducing current at some point in the circuit?

The current at any point in the circuit is the same because the current distribution in the circuit has reached a steady state (i.e., charge buildup is forbidden). Your intuition is telling you that the presence of resistance means the motion of the electrons is "damped" and that therefore some current must be, in some sense, "lost". The basic sense you have of this is right, but this "loss of current" is balanced by the driving force (the battery).
Regarding your first statement:

I've heard that resistors are used to decrease current to a particular appliance, such as in the regulator of a fan.

To be clear, adding a resistor to the circuit does reduce the current that flows through the entire circuit (as compared to the circuit without the resistor). However, the current at two points in the circuit is still the same.
Note: It should be understood, as implied by your question, that we're discussing a simple one-loop circuit. The notions mentioned above apply to more complex circuits, but would need to be generalized a little.
A: We know we can't change the mains supply voltage or the fan's coil's resistance itself to control speed (via current) so we place an external resistance in series with fan. This drops the voltage across the fan by some amount and $V(across\space fan)=I\times R(fan)$ gives the changed current in fan.
$V(across\space fan) = \frac {R(fan)\times V(mains)}{R(fan)+R(ext.)}$
A: The atoms in a resistor scatter and absorb the energy from the charge carriers in the current.  So some of the average kinetic energy of the current is converted to heat in the resistor, and the current is reduced, compared to if the resistance wasn't there.
