If you're working with an agent, you'll see two documents:
This protects the agents; it says that if you rent in one of the buildings they show you, you'll pay them the fee (unless the landlord is paying it). Not all agents use this form, and it varies by brokerage.
It's important to get a copy or take a picture of the signed fee agreement so that if you rent an apartment in a building not shown to you by the agent, you're not obligated to pay that agent's fee. A deceitful agent may write down an address you never saw together after you've left. Then he or she can go after you to collect a fee. It's totally crooked and reprehensible, but sometimes it happens, so it's just better to protect yourself. An ounce of prevention...
This document discloses whom the agent represents - either you or the owner of the property. It's required by New York State, but it's not a legal document requiring you to work with that agent, and it doesn't obligate you to pay a fee (as many renters sometimes think).
You are NOT agreeing to rent an apartment
An agent may ask you to sign an exclusivity agreement with him or her. If you sign it, you will be agreeing to work only with that agent. This is rare, but if you see it, you should feel comfortable saying no.