How do I join a NXT mining forging pool? And how do I register for payouts from the pool? I found the following pool: http://pool.nxtcrypto.org/howto.html

But I'm a bit unclear on these instructions:


  To claim your earnings, simply send an AM (can be empty or put
  whatever you want in there) to the pool account 1460178482 and after
  this AM has 1440 comfirmations, your confirmed earnings will be sent
  to you, minus NXT transfer fee.


What do they mean by "simply send an AM"? What is AM?

On the lease nxt page, it says I can attach a message. Do I just attach it during the lease transaction? Or do I have to send a separate empty message to the pool account after sending the leased funds?
I was confused by this as well, but I figured it out through trial and error. AM means arbitrary message (they should have explained this), which is a regular message you send to the forging pool through your wallet. 

First you must join the forging pool (Account Balance -> More Info -> Account Leasing). No additional message is necessary at this point.

After leasing your balance to this pool for some length of time (I waited a few weeks), you will have earned NXT from the pool's forging. When you want to collect your NXT, this is when you send the "AM" (I have found that until you send this message, you will not receive a payment).

In your NXT wallet:


Click on Messages (left navigation bar)
Click Send Message (top right tool bar)
Enter the forging pool address for Recipient (e.g. NXT-K5KL-23DJ-3XLK-22222)
Write anything for the message
Uncheck the Encrypt Message box (I did this, not sure if this is necessary)
Click Send


After your message receives 1440 confirmations (this takes a while), you will receive your share of pool earnings in your wallet from the forging pool. You need to send a new message each time you want to collect your earnings.