Let me just add a little to the answer and the link to summarize the process. When an AP boots, it needs 6 pieces of information:
IP Address
Subnet Mask
Default Gateway
AP Name
AP Group
IP address of the controller the AP will initial communicate with
All of this can be statically or dynamically obtained.
If it is a brand new AP, the IP info will be gotten using DHCP. The name will be the MAC of the Eth 0 port on the AP, the group will be 'default'.
The initial controller is obtained in the following order
statically configured
DHCP option 43/60
Aruba Discovery Protocol (ADP) multicast and broadcast
DNS
Since this is a new AP, all things will be default and you will probably discover the initial controller using ADP.
After the AP has the address of the initial controller, it communicates with it and checks if it has the same OS. If not, it does an FTP transfer, which takes about 4 minutes, and downloads the new OS. It will then reboot, with this new OS, go through the above process again, at that point it will talk to the initial controller again. This time the OS is the same, so the AP will either download the LMS-IP address for the AP group that the AP is part of (default). If there is an LMS-IP setting, the AP will communicate with that controller to download its configuration. If there is no LMS-IP setting, the AP will communicate with the controller it discovered to download its configuration. Since the AP is part of the 'default' group, it will download whatever config is assigned to the 'default' AP group.
Once this is down, the AP will display on the controller and listed with its Eth 0 MAC address as its name. You can then go in and configure it.
If you are wanting to configure it using a console connection directly into the AP, you may be prompted for a password. This is a setting that is in the AP system profile. If you want to see what the password is, you can do the following commands from the controller. The string in quotes after 'ap-console'password' is the password. Note this output has multiple profiles, so you will need to know which one you are using, or simply try both of them. You can also go to the profile and set your own console password. If you do console into APs at any time (I often do in my lab environment), I suggest that you change it to something that is easy to remember or look up.
#encrypt disable
# show running-config | begin "ap system-profile"
Building Configuration...
ap system-profile "default"
ap-console-password "44e753d6+|H333"
bkup-passwords "CR0001795!333"
!
ap system-profile "rap-ap-system"
native-vlan-id 240
rap-dhcp-server-vlan 168
rap-dhcp-dns-server 75.75.75.75
ap-console-password "9ef9d707+|333."
bkup-passwords "CR0001795!333"
I hope this helps,