Things I can do for you.

Buyer Representation
I can be the Broker for the Buyer. Altough the seller may still be the one paying my commission, I am looking out for the buyers interests. My Fiduciary responsibility is to the buyer. I am still bound to treat all parties fairly and honestly though. This requires a written agreement between myself as agent and the buyer, usually called a Buyer Broker Agreement.
Seller's Broker
The traditional way of doing business. I list a property and represent the seller. My fiduciary is to the seller only, although I am obligated to treat all parties honestly and fairly.  This agreement is also in writing, but is usually called a listing agreement, or an Exclusive Employment Agreement.
Representing both parties 
Wow! Two parties at once! Rock on! Seriously, this is a very common practice. The requirement that it be disclosed in writing is the key.  It goes like this...You see a sign on a property that my company has listed through an Excusive Employment Agreement. You want to see it, as well as other properties, and  want me to represent you as a buyer broker.  since I believe that all real estate transaction must be Win/Win situations, we can do this. It is called Limited Dual Representation.
Here are the limitations:
I will not, without written authorization, disclose to the other party that the seller will accept a price or terms other than that stated in the listng or the buyer will accept a price or terms other than that offered. There will be
          conflicts in the duties of loyalty, obedience, disclosure and confidentiality. Disclosure of confidential information            may be made only with written authorization. This does not relieve me of the responsibilty to disclose all known            facts which may materially and adversely affect the consideration to be paid by any party.